The Solar Orbiter mission, developed by the European Space Agency (ESA) with the participation of NASA, took off into orbit around the Sun on 9 February 2020. Few months later, it has already achieved its first scientific results, which were presented on 16 July in a press conference.

The mission was designed to observe the Sun from an unprecedented perspective and to study solar physics and the influence of the Sun on the interplanetary environment. The Solar Orbiter spacecraft has approached the closest point to the Sun ever reached: 77 million kilometers. During the mission it will reach even closer, at 42 million kilometers away.

Researchers from the Institute of Space Studies of Catalonia (IEEC) at the Institute of Cosmos Sciences of the Universitat de Barcelona (ICCUB) have worked on one of the instruments aboard Solar Orbiter, the Polarimetric and Helioseismic Imager (SO/PHI). The SO/PHI instrument makes high-resolution measurements of the magnetic field lines on the surface of the Sun and has allowed us to obtain the first solar magnetic field map obtained from space and without human intervention.

The SO/PHI is designed to monitor active regions on the Sun, areas with especially strong magnetic fields, which can give birth to solar flares. The ICCUB has been responsible for developing and implementing an image stabilization system (ISS) that has made it possible to compensate for the movements of the probe in order to obtain images of the required quality. "Solar Orbiter is the most complete solar mission from an instrumental point of view," explains Josep M. Gómez Cama, a researcher from IEEC at ICCUB and member of the Department of Electronic and Biomedical Engineering at the Universitat de Barcelona. Specifically, the probe incorporates ten instruments that weigh a total of 209 kg. Four of the instruments, which allow the detection of solar wind (plasma and magnetic field), radiation and emitted particles, work in situ, while the other six do so remotely and allow images to be obtained at different wavelengths and spectroscopy of the solar photosphere and corona.

The SO/PHI has been built by an international consortium (45% Germany, 42% Spain, 10% France and the rest, other countries). The Spanish part has been coordinated by the Institute of Astrophysics of Andalusia (IAA-CSIC), with the participation of ICCUB, the National Institute of Aerospace Technology (INTA), the Polytechnic University of Madrid, the University of Valencia and the Institute of Astrophysics of the Canary Islands.

In addition, researchers from the Heliospheric Physics and Space Meteorology Group (HPSWG) at ICCUB have provided scientific support to the Energy Particle Detector (EPD) team, another instrument aboard the Solar Orbiter. THe HPSWG members, experts in modeling and data analysis, developed models to predict the particle radiation environment that Solar Orbiter is facing, and developed tools to facilitate the analysis of the particle measurements it collects. According to Àngels Aran, a researcher of IEEC at ICCUB in the HPSWG group, "the results obtained by Solar Orbiter will allow us to understand the physics that connects the star with the interplanetary environment and thus adjust current models of space meteorology."

The mission is now in an initial cruising phase, which will run until November 2021. The Solar Orbiter has revolved around the Sun in an orbit with a minimum distance less than that of Mercury and outside the ecliptic, which provides a unique perspective that allows us to observe the Sun's poles. The first quality view of their magnetic field will be obtained as the Solar Orbiter elevates its orbital plane to access high latitudes. In addition, the instruments will take local and remote measurements, which will provide the first complete view of both solar physics and the heliosphere. Understanding the coupling of the Sun and the heliosphere is essential to understanding how our solar system works.

See the firsts results at the ESA's website

It will be the first time that this symposium, promoted by the European Space Agency (ESA), takes place in Spain. The event will bring to the city of Barcelona about 300 people including students, teachers and professionals from around the world. Since its first edition, the SSEA has emerged as the reference symposium in which the current state and future of space education activities in Europe and the world are discussed. The proposal has been selected by ESA, standing out among candidates from universities in other member states of the agency.

A candidacy of the space ecosystem of Barcelona

The SSEA 2021 will be organized by the three UPC schools dedicated to training and research in the space field: the School of Industrial, Aerospace and Audiovisual Engineering of Terrassa (ESEIAAT), the Barcelona School of Telecommunications Engineering (ETSETB) and the Castelldefels School of Telecommunications and Aerospace Engineering (EETAC).

In order to enrich the proposal, the organizing team was clear from the outset that other entities in the sector needed to be involved. For that reason, work is being done to include other institutions and companies, to give international visibility to the rich space ecosystem of Barcelona and to generate positive synergies between the different actors and ESA.

A student symposium for students

One of the main pillars of the SSEA 2021 is that, in addition to being aimed at students, it will also be organized by the students themselves, the engineers, and scientists who will lead the future of the space sector in Europe. Thus, the organizing team has a careful balance between professionals, master's students and undergraduate students. The proposal also places special emphasis on promoting Europe’s space education in the world and on achieving goals of equity, gender equality, diversity and sustainability. The visit of hundreds of participants to Barcelona will also be a great opportunity to collaborate in the reconstruction of the social and productive fabric of the city on the post-COVID-19 stage.

A bridge to the university

The following article is written by R. Ballabriga, D. Gascón and and M. Campbell, and was published at the newsletter of the EP department at CERN.

Precise time tagging is a hot topic in High Energy Physics and in other fields. A number of detector technologies are available but there are few multi-channel front-end ASICs capable of providing time tagging in the region of 10ps. This article describes two developments that are going on within the microelectronics section of the Electronics Systems for the Experiments group (ESE-ME). Both the FastIC and the FastICpix developments are based on a collaboration between ESE-ME and the ICCUB.

The collaboration started in 2016 after the authors of this note co-organized a one-week summer school in Barcelona about solid-state semiconductor radiation detectors. That school, called the first Barcelona Techno Week, was attended by more than 60 students, mainly from Europe but also from the United States, Canada and even New Zealand. We had excellent lecturers including Erik Heijne (CERN), Paul O’Connor (BNL), Angelo Rivetti (INFN-Torino) or Angel Rodriguez and Ricardo Carmona from University of Sevilla, who covered radiation detectors from the basic principles to the state of the art, from interaction of radiation with matter to applications. That was the school we would have liked to have attended when we started in the field of design of electronics for radiation detectors.

After that organizational experience, the authors decided to start the FastIC project to design an Application Specific Integrated Circuit (ASIC), in 65nm CMOS technology, for the readout of fast timing detectors with an intrinsic gain of ~10⁵-10⁶ (examples of these detectors are Silicon PhotoMultipliers, Micro Channel Plates or Photomultiplier tubes). The first prototype was submitted to fabrication in May this year and includes a fully functional design with 8 single-ended channels. The FastIC chip is designed to replace the NINO, an ASIC implemented in 250nm CMOS, and to improve on its performance. The NINO ASIC [1] was designed in 2004 for the ALICE Time of Flight detector and, to the credit of its designers, it is still today a reference for the readout of fast detectors with low jitter. However, there are a few limitations: the energy measurement, based on the Time-over-Threshold method is non linear, its power consumption is large and it does not have build-in testing capabilities.

As NINO is widely used outside of CERN we were able to obtain financial support for the project from the KT fund. This funding allowed us to hire a PhD student, Jose Maria Fernandez-Tenllado, and to contribute financially to the submission of two Multi-Project Wafer (MPW) runs. As chance would have it, the authors met Jose Maria Fernandez-Tenllado at the first Barcelona Techno Week. Jose subsequently came to EPFL for his Masters Thesis. While in Lausanne, he visited our CERN labs at the time we had an opening for a PhD position to work in the FastIC design and to which he successfully applied.

There are many challenges when designing electronics for the readout of fast detectors. One of the challenges is related to the interconnection between the sensor and the readout ASIC. The jitter, that is the uncertainty in the time measurement, has the following expression:

α_t = α_n / (ds/dt)

Where α_n is the noise of the system and ds/dt is the derivative of the signal (which can be a voltage or a current signal). The intrinsic inductance of the interconnection filters the high frequency components of the signal delivered by the sensor reducing the slope of the input current pulse entering into the front-end [2]. Since the jitter is inversely proportional to the slope of the signal, it is degraded by the effect of the inductance. The input capacitance of the sensor is another factor that limits the slope of the signal at the preamplifier input. A careful study has to be done in order to optimize the input impedance of the electronics to avoid ringing in the signals due to resonances of the input network and the study also has to address considerations related to the optimum bandwidth of the input front-end. Designing for a bandwidth above this optimum there is a penalty in the jitter because of an excess in noise and in power consumption [3]. The large range in the input capacitance of the detectors and the input dynamic range for detectors like SiPMs (from a few μA to mA) make the design of the input stage and the signal processing very challenging (e.g. the input capacitance for MCPs can be in the order of ~10pF whereas the input capacitance for SiPMs can be from ~100pF to ~1nF).

Another challenge consists in the limitations imposed by the choice of the technological node for manufacturing the ASIC. Trends in the microelectronics industry and the need for increased signal processing speed and performances oblige the radiation instrumentation community to continue to follow Moore’s Law in the development of front-end electronics. Moreover, the adoption of new technologies can add significant benefits and open new applications. Therefore, the new front-end has been designed in the most recent CMOS technology to which we have regular access (65nm CMOS). However, each new technology node requires a significant effort to understand how high performance analog designs can be implemented. The main challenges imposed by the very deep submicron technology have been, in particular, the reduced power supply voltage (1.2V) that results in a reduction of the dynamic range, the reduction in the intrinsic gain of the transistor and increased gate leakage currents with respect to previous technological nodes.

FastIC

The FastIC chip reads out the signal delivered by the sensor and processes it in a current mode method. A block diagram is shown in Figure 1. The architecture is based on the HRflexToT chip [4].

Figure 1.Block diagram of the FastIC ASIC channel when programmed in a single ended architecture. The Input Stage, the Time, Energy and Trigger channels and the Output driver are shown.

The input stage generates three replicas of the incoming signal, the weight of each replica being different. The first replica, with the highest weight, corresponds to the timing signal that is sent to a fast current discriminator which compares the signal with a programmable threshold. This threshold can be set at level below the charge delivered from the sensor when a single photoelectron is detected. The leading edge of the signal at the comparator output retains the information of the time of arrival of the detected particle. The chip can be programmed to output this signal for each channel. It also outputs a fast-OR combining the timing signals of all the channels.

The second replica is processed by some circuitry in order to measure the deposited energy in the sensor. The processing chain contains a transimpedance amplifier, a shaper (with a selectable peaking time, the nominal being ~25ns-50ns), a peak detector and hold (PDH) and a discriminator that compares the output of the PDH with a ramp. The time duration of the digital pulse at the output of this discriminator is proportional to the charge delivered by the sensor.

The third replica is used for the trigger signal whose threshold is typically set to be higher than the threshold of the timing channel. Two trigger signals can be generated. The Low Level Trigger and the Cluster Level Trigger. The Low Level Trigger is the OR of the output of the comparators of the trigger channels and the Cluster Level Trigger compares the sum of the signals deposited in all the channels in a chip with a separate threshold. These trigger signals can be used to start the ramp generator for the energy to time conversion. Alternatively, the OR of the fast timing channels or a pulse fed externally into the chip can also be used for this purpose.

At the output of the time and energy processing branches, the channel can be programmed to provide (1) The Time-Of-Arrival information only, (2) the Time over Threshold information or (3) a combination of the two. In the first case, the energy branch is bypassed and as a consequence, the pulses at the fast discriminator output can be very short, the maximum flux that can be processed by the channel being only dependent on the signal of the detector itself. In the latter case, the channel generates two pulses for an incoming input signal. The first pulse’s rising edge contains the information of the ToA and the second pulse’s width contains the information on the linear energy measurement. The maximum count rate that the chip can process in this mode is ~2MHz.

The input stage can be programmed to work in either positive or negative polarity. In the case of a detector with a differential output, the 8 single ended channels can be reconfigured into 4 differential channels. It is also possible to combine 4 channels and sum their signals at the ouput of the input stage. This active summation functionality is integrated to explore the impact of segmenting large SiPMs (with large capacitance) into smaller ones to achieve lower jitter while covering large detector areas. The expected performance of the chip is presented in Table 1.

In FastIC the readout channels are laid out in a linear way and the chip inputs are wire-bonded to a PCB or to a package. This interconnection scheme with its associated added inductance limits the time performance of the system as described above. Also, the large intrinsic capacitance in sensors like Silicon Photomultipliers leads to a reduction of the input signal amplitude in current sensing and processing circuits. The combination of both effects limits the slew rate of the signal and as a consequence the system suffers from an increased jitter. This lead the design team to propose a new sensor architecture whereby the sensor and readout electronics are intimately connected: the FastICpix concept.

FastICpix

FastICpix is a detector architectural study, funded by an ATTRACT phase I grant, which aims at at 10ps time resolution by proposing a new hybrid sensor and readout electronics. The proposed hybrid interconnection minimizes the effects of parasitic components associated with interconnects and enables sensor segmentation to reduce dramatically the effective capacitance.

The FastICpix sensor concept is based on the readout of groups of Single Photon Avalanche Diodes (SPADs) by a readout chip. The connection is done using bump bonding (with pitch ~300μm). The SPADs are implemented in a process optimized for light detection and are Front-Side Illuminated. They are grouped in clusters and connected to the back-side of the sensor chip by means of a TSV last process [5]. A Redistribution Layer (RDL) layer is also implemented to connect the TSV with the bump-bonding pad. The bonding pad is connected to a readout circuit designed in 65nm CMOS technology. The reduction of the input capacitance due to the interconnection and due to the segmentation results in a larger current signal at the input of the front-end, which helps to reduce the jitter. The pixels are configured so that the signals from different sensor elements can be summed. This means that the granularity is configurable. It will be possible to trade off between time resolution, spatial resolution, power and data rate to optimize the operation of the hybrid sensor to different applications. The readout ASIC is designed abuttable on 4 sides to build large seamless detection areas.

The Phase I FastICpix project deliverables consists of a feasibility study based on a full Monte Carlo simulation including a physical simulation of the scintillator crystal, the sensor and the readout electronics. The study provides a framework to globally optimize the detector system for a given application (e.g. Positron Emission Tomography).

The work on the integration of the sensor elements with the analog front-end electronics has shown that segmenting large area SiPMs and actively summing the signals in adjacent channels helps improving the Single Photon Time Resolution (SPTR).

The design of the digital part of the chip is also challenging and it is based on the lessons learnt in the Timepix3 [6] and Timepix4 [7] chips. In order to time stamp the incoming photons, a TDC is implemented on each pixel. The TDC is based on a ~2GHz (nominal) ring oscillator with 12 phases that is started with the arrival of a signal and is stopped at the following rising edge of the system clock (≤100MHz). The ring oscillator is active a small fraction of time in order to minimize power consumption. System clock is interpolated in two steps: first, a counter increases its value with every oscillation of the ring, and second, the internal phases of the ring oscillator are latched at the rising edge of the system clock in order to obtain a fine time measurement (20-ps time bin). The study on the TDC has been done in collaboration with the group of Angel Rodriguez and Ricardo Carmona from University of Sevilla whom the authors met in the framework of the Barcelona Techno Week in 2016 and who assigned a PhD student in the last months of his doctoral studies, Franco Bandi, to work on the FastICpix project.

A study on how to distribute the system very low-jitter clock to all the pixel elements with low power consumption is in progress. This study is based on the Timepix4 Clock Distribution Network (CDN) architecture, which consists of a Digital Delay Locked Loop in which the delay line is distributed along two columns of pixels, a phase comparator and a control system located at the base of every double column [7]. The novelty in the approach for FastICPix is that the control of every delay cell in the line is done individually, which provides a finer adjustment of the delay of the line and thus reduces the systematic error associated to the CDN.

Summary

The FastIC project aims at designing an ASIC with a linear array of channels for sensor readout. It provides a fast timing signal as well as signal processing to obtain a linear energy to time conversion. This chip could be read out by the picoTDC, a Time-To-Digital Converter designed at the microelectronics section at CERN. As well as High Energy Physics the chip could find applications in fields such as Positron-Emission-Tomography (PET), LIDAR and biology.

The FastICPix project aims at 10ps time resolution by proposing a new hybrid sensor and readout electronics. Its architecture can also be used with other types of sensors like Micro Channel Plates (MCPs) and other fast detectors with intrinsic amplification.

Many of the people participating in the two projects presented in this article have met while preparing training activities for younger colleagues. Organizing the Barcelona Techno Week event was a good way to prepare teaching material about the basic principles and the state of the art in our field and share it with other colleagues from our organizations and from external ones. But it also had some other side effects. It proved to be a way to recruit good students and also led us to establish personal links and solid collaborations.

The NASA/ESA Hubble Space Telescope was used to conduct a three-year study of the crowded, massive and young star cluster Westerlund 2, in the first time that astronomers have analysed an extremely dense star cluster to study which environments are favourable to planet formation. Our astronomer and ICREA professor Mark Gieles contributed to the interpretation of the results.

The researchers found that the material encircling stars near the cluster’s centre is mysteriously devoid of the large, dense clouds of dust that would be expected to become planets in a few million years. Their absence is caused by the cluster’s most massive and brightest stars that erode and disperse the discs of gas and dust of neighbouring stars.

This time-domain study from 2016 to 2019 sought to investigate the properties of stars during their early evolutionary phases and to trace the evolution of their circumstellar environments [1]. Such studies had previously been confined to the nearest, low-density, star-forming regions. Astronomers have now used the Hubble Space Telescope to extend this research to the centre of one of the few young massive clusters in the Milky Way, Westerlund 2, for the first time.

Astronomers have now found that planets have a tough time forming in this central region of the cluster. The observations also reveal that stars on the cluster’s periphery do have immense planet-forming dust clouds embedded in their discs. To explain why some stars in Westerlund 2 have a difficult time forming planets while others do not, researchers suggest this is largely due to location. The most massive and brightest stars in the cluster congregate in the core. Westerlund 2 contains at least 37 extremely massive stars, some weighing up to 100 solar masses. Their blistering ultraviolet radiation and hurricane-like stellar winds act like blowtorches and erode the discs around neighbouring stars, dispersing the giant dust clouds.

Professor Mark Gieles, member of the Institute of Cosmos Sciences, joined this research due to his stellar dynamics and binaries expertise contributing to the interpretation of the results.

“Basically, if you have monster stars, their energy is going to alter the properties of the discs,” explained lead researcher Elena Sabbi, of the Space Telescope Science Institute in Baltimore, USA. “You may still have a disc, but the stars change the composition of the dust in the discs, so it’s harder to create stable structures that will eventually lead to planets. We think the dust either evaporates away in 1 million years, or it changes in composition and size so dramatically that planets don’t have the building blocks to form.”

Westerlund 2 is a unique laboratory in which to study stellar evolutionary processes because it’s relatively nearby, is quite young, and contains a rich stellar population. The cluster resides in a stellar breeding ground known as Gum 29, located roughly 14 000 light-years away in the constellation of Carina (The Ship’s Keel). The stellar nursery is difficult to observe because it is surrounded by dust, but Hubble’s Wide Field Camera 3 can peer through the dusty veil in near-infrared light, giving astronomers a clear view of the cluster. Hubble’s sharp vision was used to resolve and study the dense concentration of stars in the central cluster.

“With an age of less than about two million years, Westerlund 2 harbours some of the most massive, and hottest, young stars in the Milky Way,” said team member Danny Lennon of the Instituto de Astrofísica de Canarias and the Universidad de La Laguna. “The ambient environment of this cluster is therefore constantly bombarded by strong stellar winds and ultraviolet radiation from these giants that have masses of up to 100 times that of the Sun.”

Sabbi and her team found that of the nearly 5000 stars in Westerlund 2 with masses between 0.1 and 5 times the Sun’s mass, 1500 of them show dramatic fluctuations in their luminosity, which is commonly accepted as being due to the presence of large dusty structures and planetesimals. Orbiting material would temporarily block some of the starlight, causing fluctuations in brightness. However, Hubble only detected the signature of dust particles around stars outside the central region. They did not detect these dips in brightness in stars residing within four light-years of the centre.

“We think they are planetesimals or structures in formation,” Sabbi explained. “These could be the seeds that eventually lead to planets in more evolved systems. These are the systems we don’t see close to very massive stars. We see them only in systems outside the centre.”

Thanks to Hubble, astronomers can now see how stars are accreting in environments that are like the early Universe, where clusters were dominated by monster stars. So far, the best known nearby stellar environment that contains massive stars is the starbirth region in the Orion Nebula. However, Westerlund 2 is a richer target because of its larger stellar population.

“Westerlund 2 gives us much better statistics on how mass affects the evolution of stars, how rapidly they evolve, and we see the evolution of stellar discs and the importance of stellar feedback in modifying the properties of these systems,” said Sabbi. “We can use all of this information to inform models of planet formation and stellar evolution.”

This cluster will also be an excellent target for follow-up observations with the upcoming NASA/ESA/CSA James Webb Space Telescope, an infrared observatory. Hubble has helped astronomers identify the stars that have possible planetary structures. Withthe Webb telescope, researchers will be able to study which discs around stars are not accreting material and which discs still have material that could build up into planets. Webb will also study the chemistry of the discs in different evolutionary phases and watch how they change, to help astronomers determine what role the environment plays in their evolution.

“A major conclusion of this work is that the powerful ultraviolet radiation of massive stars alters the discs around neighbouring stars,” said Lennon. “If this is confirmed with measurements by the James Webb Space Telescope, this result may also explain why planetary systems are rare in old massive globular clusters.”

This video shows a pan across the new image of star cluster Westerlund 2, taken by the NASA/ESA Hubble Space telescope and released to celebrate its 25th year in orbit.

Music: Johan Back Monell (www.johanmonell.com)

Notes
[1] These observations were made under Hubble observing programs #14087, #15362, and #15514.

More information
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The international team of astronomers in this study consists of E. Sabbi, M. Gennaro, J. Anderson, V. Bajaj, N. Bastian, J. S. Gallagher, III, M. Gieles, D. J. Lennon, A. Nota, K. C. Sahu, and P. Zeidler.

Image credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

Links

• Images of Hubble
• Hubblesite release
• Science paper
• Westerlund 2 3D Tactile Print

Luca Tagliacozzo, together with colleagues Titas Chanda and Jakub Zakrzewski from Jagiellonian University in Cracow, and Maciej Lewenstein from ICFO, report on a new theoretical method to understand bosonic behavior in quantum simulations.

The new article, recently published in the journal Physical Review Letters, opens a path towards quantum simulations of quantum gauge theories in novel, unexplored regimes.

Relativistic quantum gauge theories are fundamental theories of matter describing nature. Paradigmatic examples are quantum electrodynamics (describing electromagnetic interactions of charged particles and photons), chromodynamics (describing strong interactions of quarks and gluons), and the Standard Model, unifying the latter two with the weak interactions.

Despite enormous progress in our understanding of quantum gauge theories, the questions concerning the behaviors of systems described by such theories in the presence of strong correlations remain widely open; from the very nature of the quark confinement, to the behavior of quark-gluon-plasma at high densities and temperatures. Moreover, quantum out-of-equilibrium dynamics of quantum gauge theories is out of reach of the present computers.

For these reasons, there is a lot of effort to design and investigate quantum simulators of such systems. The paradigmatic model of quantum gauge theory in one spatial dimension and time is the Schwinger model, in which “charged” electrons (fermions) interact with photons (bosons) in one dimension. Since quantum simulations with fermions are notoriously difficult, the team proposes a bosonic version of the Schwinger model.

Figure 1. (a) In the lattice version of bosonic Schwinger Model (BSM), sites are occupied by two kinds of bosons, corresponding to particles (red dots) and antiparticles (blue dots), which are coupled to U(1) gauge fields residing on bonds. Tunneling of bosons across a given bond change the internal state of corresponding gauge field as dictated by arrows. (b) Time-dynamics of BSM is greatly affected by strong confinement, where the light-cone of the particles bends inwards, producing exotic asymptotic states made of a central core of strongly correlated bosons and external regions populated by free mesons. Image Credit: Titas Chanda

Using state-of-the-art methods of theoretical physics, they investigated in their work how the bosonic matter behaves when it is driven out-of-equilibrium by creating a pair of particle and antiparticle on top of the vacuum of the system.

They obtain three remarkable results for the understanding of quantum gauge theories in general. In the first place, the bosons undergo evolution dominated by strong confinement of charges, responsible for only a partial screening of electric field, even in the massless limit. Moreover, the extended “meson” formed by the two charges and the electric-flux tube connecting them is very robust, leaving a strong footprint in the entanglement of the system. And finally, the systems fails to thermalize and generate exotic states at long times, characterized by two distinct space-time regions; one external region made by thermal mesons, and a central region between the two initial charges where their quantum correlations obey the area-law of entanglement.

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Read the whole article at Physical Review Letters.

On the night of April 10, the European Space Agency's (ESA) BepiColombo probe completed its first and only approach to Earth, passing less than 12,700 km from the surface of our planet, on its way to its final destination: Mercury. The space mission made a flyby to take advantage of its gravitational impulse. This was the only time that the space mission will come close to our planet on its journey to Mercury.

Launched in 2018, BepiColombo is on its seven-year journey to the smallest and least explored planet orbiting the Sun, which contains important clues about the formation and evolution of the entire Solar System. The mission is a joint effort between ESA and the Japan Aerospace Exploration Agency (JAXA), carried out under ESA's leadership. It is the first European mission to Mercury, where only two NASA probes have arrived.

This approach is the first of nine flights that, together with the solar propulsion system the probe carries on board, will help it reach its orbit around Mercury. The next two flights will take place on Venus and the other six on Mercury itself. Scientists will use the data collected during the flyby, which includes images of the Moon and measurements of the Earth's magnetic field as the spacecraft passed by at full speed, to calibrate the instruments that, starting in 2026, will investigate Mercury to solve the mystery of how it formed, make a cartographic map and study the magnetosphere. In addition, ESA's Planetary Defence Office is using this flight as proof of its ability to coordinate asteroid observations with a non-nil probability of impacting our planet.

ESA's NEO Coordination Centre (NEOCC) coordinated many telescopes from around the world to track the probe's position and brightness as it passed over the Earth. The Joan Oró Telescope (TJO) is one of the telescopes that participated in the monitoring of the BepiColombo probe as it passed very close to the Earth. The scientific coordination of the telescope is carried out by scientists from the Institut d'Estudis Espacials de Catalunya (IEEC). Toni Santana-Ros, from our institute, has led the TJO observations of the flyby. A set of 98 images, 20 seconds exposure time each, taken with the TJO on 10 April 2020 is shown in video format.

"Observing an object with an apparent movement as fast as the BepiColombo is quite a challenge for a telescope. The TJO has allowed us to track the object up to 6 days after approaching the Earth, when the object already had a magnitude of 20.5. The TJO is certainly one of the few telescopes on the peninsula capable of making this type of observation," said Toni Santana-Ros.

The OAdM, of the Institute of Space Studies of Catalonia (IEEC) and whose director is the ICCUB researcher Marc Ribó, is dedicated to carrying out research programmes in space sciences and satellite operations control. The TJO and the entire OAdM in general, including the TFRM telescope, participate in international near-Earth monitoring programmes financed by the EU and ESA, among others. These programmes are dedicated to the detection and tracking of both near-solar system objects (NEOs) and artificial satellites.

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You will find more information on the BepiColombo mission at the European Space Agency, and details about the Joan Oró Telescope at the Montsec Astronomical Observatory.

A team of ICCUB researchers led by Alfred Castro-Ginard has found 582 new open clusters, using the data from the second release of the Gaia mission.

Open clusters are groups of gravitationally bound stars, that were formed in the same event – so they have the same chemical composition and age – and share a common position and proper motion. Those open clusters are fundamental objects in galaxies, and key for the understanding of the structure and evolution of the Milky Way. While young open clusters allow researchers to trace the star forming regions and to understand the star forming mechanisms, intermediate and old open clusters inform about the stellar processes and evolution of the Galactic disc.

The study and search for open clusters has been boosted by the second release of the Gaia mission data (DR2), which contained information about precise astrometric measurements of more than 1.3 billion stars. Since its publication, several studies have been finding new open clusters, but they were computationally limited to analyzing particular regions of the galactic disc,or dividing the search areas into smaller ones with a limited number of stars.

The ICCUB team, led by researcher Alfred Castro-Ginard, has been developing a new methodology, which has been published in two previous studies in 2018 and 2019. In 2018, they presented the method and applied it to a small data set. Later, they used it in a certain region of the galaxy, so they could test how the method worked with the Gaia data and in different parts of the galaxy. Castro-Ginard explains, “Before Gaia, we didn’t have a homogenous methodology to study and detect those objects, because we didn’t have such a big and precise data catalogue. That’s why we chose a machine-learning based method, which automatizes and allows the study of a big volume of data.”

Figure 1. Clusters distribution in an X, Y projection. In red, the previously known open clusters, and in black, dots representing the new ones - where size is proportional to the number of members.

They used the machine-learning based methodology to search for overdensities across the whole Galactic disc, using an unsupervised clustering algorithm -named DBSCAN – which pointed to several overdensities as plausible candidates for open clusters. Then, they confirmed those candidates as open clusters through a deep learning artificial neural network, which recognized isochrone patterns in the colour and magnitude.

“Before this methodology, they were around 1200 open clusters confirmed by Gaia”, says Castro-Ginard. ”Using Gaia’s data and our methodology, we have found more than 650 new clusters - 23 detected in 2018, 53 in 2019 and now, 528 more. This has improved and increased the catalogue, which now contains more than 2000 open clusters.”

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You can read the whole article at Astronomy & Astrophysics.

See related articles:

Castro-Ginard et al., 2018. “A new method for unveiling open clusters in Gaia. New nearby open clusters confirmed by DR2”, Astronomy & Astrophysics, 618, id.A59.

Castro-Ginard et al., 2019. “Hunting for open clusters in Gaia DR2: the Galactic anticentre”, Astronomy& Astrophysics, 627, id.A35.

The following is based on an article that originally appeared on MIT News.

Asteroids come in all shapes and sizes, and now astronomers at MIT and elsewhere have observed an asteroid so heavily cratered that they are dubbing it the “golf ball asteroid.”

The asteroid is named Pallas, after the Greek goddess of wisdom, and was originally discovered in 1802. Pallas is the third largest object in the asteroid belt, and is about one-seventh the size of the moon. For centuries, astronomers have noticed that the asteroid orbits along a significantly tilted track compared with the majority of objects in the asteroid belt, though the reason for its incline remains a mystery.

In a paper published today in Nature Astronomy, researchers reveal detailed images of Pallas, including its heavily cratered surface, for the first time.

The researchers suspect that Pallas’ pummeled surface is a result of the asteroid’s skewed orbit: While most objects in the asteroid belt travel roughly along the same elliptical track around the sun, much like cars on a race course, Pallas’s tilted orbit is such that the asteroid has to smash its way through the asteroid belt at an angle. Any collisions that Pallas experiences along its way would be around four times more damaging than collisions between two asteroids in the same orbit.

“Pallas’ orbit implies very high-velocity impacts,” says Michaël Marsset, the paper’s lead author and a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “From these images, we can now say that Pallas is the most cratered object that we know of in the asteroid belt. It’s like discovering a new world.”

Marsset’s co-authors include collaborators from 21 research institutions around the world.

“A violent history”

The team, led by principal investigator Pierre Vernazza from the Laboratoire d'Astrophyisque de Marseille in France, obtained images of Pallas using the SPHERE instrument at the European Southern Observatory’s Very Large Telescope (VLT), an array of four telescopes, each with an 8-meter-wide mirror, situated in the mountains of Chile. In 2017, and then again in 2019, Marsset and his colleagues reserved one of the four telescopes several days at a time to see if they could capture images of Pallas at a point in its orbit that was closest to Earth.

The team obtained 11 series of images over two observing runs, catching Pallas from different angles as it rotated. After compiling the images, the researchers generated a 3D reconstruction of the shape of the asteroid, along with a crater map of its poles, along with parts of its equatorial region.

ICCUB’s researcher Toni Santana-Ros coordinated during the project’s first year a photometric follow-up of Pallas. They processed the light-curve data, which another team used to build a 3D model of the asteroid. “Combining both adaptive optics and the 3D shape model provides information about certain areas of the object that might remain non-visible in the optical images,” Santana-Ros explains. “Furthermore, using the model together with the images allows making an escalation of the object, and then we can measure certain aspects such as its radius or density. For instance, we have obtained a more accurate Pallas’ density value, which was still under discussion”. Santana- Ros is currently a postdoc researcher in Solar System & Minor Bodies at our Institute.

In all, they identified 36 craters larger than 30 kilometers in diameter — about one-fifth the diameter of Earth’s Chicxulub crater, the original impact of which likely killed off the dinosaurs 65 million years ago. Pallas’ craters appear to cover at least 10 percent of the asteroid’s surface, which is “suggestive of a violent collisional history,” as the researchers state in their paper.

To see how violent that history likely has been, the team ran a series of simulations of Pallas and its interactions with the rest of the asteroid belt over the last 4 billion years — about the age of the solar system. They did the same with Ceres and Vesta, taking into account each asteroid’s size, mass, and orbital properties, as well as the speed and size distributions of objects within the asteroid belt. They recorded each time a simulated collision produced a crater, on either Pallas, Ceres, or Vesta, that was at least 40 kilometers wide (the size of most of the craters that they observed on Pallas).

They found that a 40-kilometer crater on Pallas could be made by a collision with a much smaller object compared to the same size crater on either Ceres or Vesta. Because small asteroids are much more numerous in the asteroid belt than larger ones, this implies that Pallas has a higher likelihood of experiencing high-velocity cratering events than the other two asteroids.

“Pallas experiences two to three times more collisions than Ceres or Vesta, and its tilted orbit is a straightforward explanation for the very weird surface that we don’t see on either of the other two asteroids,” Marsset says.

A fragmented family

The researchers made two additional discoveries from their images: a curiously bright spot in the asteroid’s southern hemisphere and an extremely large impact basin along the asteroid’s equator.

For the latter discovery, the team looked for explanations for what may have caused such a large impact, estimated to be about 400 kilometers wide.

They simulated various impacts along the equator, and also tracked the fragments that likely were carved out of Pallas’ surface and spewed out into space as the result of each impact.

From their simulations, the team concludes that the large impact basin was likely the result of a collision about 1.7 billion years ago by an object between 20 to 40 kilometers wide, that subsequently ejected fragments of the asteroid out into space, in a pattern that, as it happens, matches a family of fragments that have been observed to trail after Pallas today.

“The equator excavation could very well relate to the current Pallas family of fragments,” says study co-author Miroslav Brož of the Astronomical Institute of Charles University in Prague.

As for the bright spot discovered in Pallas’ southern hemisphere, the researchers are still unclear as to what it might be. Their leading theory is that the region could be a very large salt deposit. From their three-dimensional reconstruction of the asteroid, the researchers estimated Pallas’ volume, and, combined with its known mass, they calculate that its density is different from either Ceres or Vesta, and that it likely originally formed from a mixture of water ice, and silicates. Over time, as the ice in the asteroid’s interior melted, it likely hydrated the silicates, forming salt deposits that could have been exposed following an impact.

One supporting piece of evidence for this hypothesis may come from closer to Earth. Each December, stargazers can view a dazzling display known as the Geminids — a shower of meteors that are fragments of the asteroid Phaethon, which itself is thought to be an escaped fragment of Pallas that eventually made its way into Earth’s orbit. Astronomers have long noted a range of sodium content in the Geminid showers, which Marsset and his colleagues now posit may have originated from salt deposits within Pallas.

“People have proposed missions to Pallas with very small, cheap satellites,” Marsset says. “I don’t know if they would happen, but they could tell us more about the surface of Pallas and the origin of the bright spot.”

This research was supported, in part, by NASA, the French Ministry of Defense, Aix-Marseille University, and the European Union’s Horizon 2020 research and innovation program.

Reprinted with permission of MIT News.

A team of ICCUB researchers has worked on one of the ten facilities of the Solar Orbiter. This instrument is called SO/PHI (Polarimetric and Helioseismic Imager), which will provide high precision measures of the magnetic field of the solar photosphere. The team took care of the development and implementation of an Image Stabilization System (ISS), which will enable the balance of the probe movements to get images with the required quality. Furthermore, the researchers from the Heliospheric Physics and Space Weather (HPSWG) of the UB provided scientific support to the team of the Energetic Particle Detector (EPD). The members of HPSWG, experts in data analysis and modelling, developed models to predict the environment of particle radiation the Solar Orbiter will find, and are working on tools to ease the analysis of the measures of the particles it will collect.

Read the whole article at the University of Barcelona News

The brightening of the star,located in the Cygnus constellation, was first spotted in August 2016 by the Gaia Photometric Science Alerts programme. This system, maintained by the Institute of Astronomy at the University of Cambridge, UK, scans daily the huge amount of data coming from Gaia and alerts astronomers to the appearance of new sources or unusual brightness variations in known ones, so that they can quickly point other ground and space-based telescopes to study them in detail. The phenomena may include supernova explosions and other stellar outbursts.

In this particular instance, follow-up observations performed with more than 50 telescopes worldwide revealed that the source – since then named Gaia16aye – was behaving in a rather strange way. The pair consists of two rather small stars, with 0.57 and 0.36 times the mass of our Sun, respectively. Separated by roughly twice th Earth-Sun distance, the stars orbit around their mutual centre of mass in less than three years.

We saw the star getting brighter and brighter and then, within one day, its brightness suddenly dropped,” says Lukasz Wyrzykowski from the Astronomical Observatory at the University of Warsaw , who is one of the scientists behind the Gaia Photometric Science Alert programme. “This was a very unusual behaviour. Hardly any type of supernova or other star does this.”

Lukasz and collaborators soon realized that this brightening was caused by gravitational microlensing – an effect predicted by Einstein’s theory of general relativity, caused by the bending of space-timenear very massive objects, like stars or black holes.

When such a massive object, which may be too faint to be observed from Earth, passes in front of another, more distant source of light, its gravity bends the fabric of spacetime in its vicinity. This distorts the path of light rays coming from the background source – essentially behaving like a giant magnifying glass. Gaia16aye is the second micro-lensing event detected by ESA’s star surveyor. However, the astronomers noticed it behaved strangely even for this type of event.

“If you have a single lens, caused by a single object, there would be just a small, steady rise in brightness and then there would be a smooth decline as the lens passes in front of the distant source and then moves away,” says Lukasz. “In this case, not only did the star brightness drop sharply rather than smoothly, but after a couple of weeks it brightened up again, which is very unusual. Over the 500 days of observation, we have seen it brighten up and decline five times.”

This sudden and sharp drop in brightness suggested that the gravitational lens causing the brightening must consist of a binary system – a pair of stars, or other celestial objects, bound to one another by mutual gravity. The combined gravitational fields of the two objects produce a lens with a rather intricate network of high magnification regions. When a background source passes through such regions on the plane of the sky, it lights up, and then dims immediately upon exiting it. From the pattern of subsequent brightenings and dimmings, the astronomers were able to deduce that the binary system was rotating at a rather fast pace.

The long period of observations,which lasted until the end of 2017, and the extensive participation of ground-based telescopes from around the globe enabled the astronomers to gather a large amount of data – almost 25 000 individual data points. In addition, the team also made use of dozens of observations of this star collected by Gaia as it kept scanning the sky over the months. These data have undergone preliminary calibration and were made public as part of the Gaia Science Alerts programme.

ICCUB researcher Josep Manel Carrasco has coordinated the participation of the Observatori del Montsec in the Gaia Science Alerts programme since 2005. The group has contributed with up to 2000 observations, obtained with the Joan Oró Telescope (TJO). That represents the 9% of the total photometric observations of Gaia16aye, which were obtained through more than 50 observatories. “The detection of binary systems through microlensing – such as Gaia16aye – allows measuring the mass and orbital parameters of those binary systems”, Carrasco explains. “The same method that we used in Gaia16aye could be applied in the future to search for new multiple systems, regardless of their mass, so it might lead to new discoveries of very low-mass bodies such as planets, or very high-mass objects as black holes, that are currently invisible for the optical telescopes.”

“If it wasn’t for Gaia scanning the whole sky and then sending the alerts straight away, we would never have known about this microlensing event,” says co-author Simon Hodgkin from the University of Cambridge, who leads the Gaia Science Alerts programme. “Maybe we would have found it later, but then it might have been too late.”

More information

“Full Orbital Solution for the Binary System in the Northern Galactic Disk Microlensing Event Gaia16aye”by L. Wyrzykowski et al is published in Astronomy and Astrophysics.

ESA press release - Global Gaia campaing reveals secrets of stellar pair