ATLAS searches for rare Higgs boson decays into a photon and a Z boson

CERN - ATLAS Experiment logo.

April 21, 2020

Image above: Event display of a candidate Higgs-boson decay to a photon and a Z boson, where the Z boson decays to two muons (shown in red). Green rectangles correspond to energy deposits in cells of the electromagnetic calorimeter, while yellow rectangles correspond to energy deposits in cells of the hadron calorimeter. (Image: ATLAS Collaboration/CERN).

The Higgs boson was discovered by the ATLAS and CMS Collaborations at CERN’s Large Hadron Collider (LHC) in 2012 through its decays into pairs of pho­tons, W bosons and Z bosons. Since then, physicists at these experiments have gained great insight into the properties of the Higgs boson through the study of its different production and decay processes. Decays to pairs of tau leptons and bottom quarks were established, as was the coupling to top quarks. However, the question remains whether the Higgs boson may also interact with yet-unknown particles or forces.

Eight years after its discovery, ATLAS has observed nearly 90% of all Higgs-boson decays predicted by the Standard Model. A rare decay of the Higgs boson that has yet to be seen is that to a Z boson and a photon (Zγ). This decay is of particular interest to physicists as it proceeds through processes involving heavy “virtual” (possibly new) particles, which could modify its rate.

The ATLAS Collaboration has just released a new result searching for the Higgs-boson decay to Zγ. This result uses the full LHC Run-2 dataset, analysing almost four times as many Higgs-boson events as the previous ATLAS result.

The new ATLAS result examines the full dataset collected during Run 2 of the LHC in search of the rare Higgs boson decay to a Z boson and a photon.

According to the Standard Model, 0.15% of Higgs bosons decay to Zγ – a rate comparable to the Higgs-boson decay to two photons, one of the discovery channels. However, unlike photons, Z bosons decay almost instantly and cannot be directly observed. Instead, the Z bosons are reconstructed through their decays into electron or muon pairs. As less than 7% of Z bosons decay in this way, only a tiny expected signal of about 1 in 10,000 Standard Model Higgs bosons can be probed.

Graphic above: Figure 1: Weighted Zγ mass distribution of events satisfying the H→Zγ selection in data. Events are weighted by the expected signal and background in a Zγ mass window containing 68% of the expected signal. The solid blue curve shows the fitted signal plus background model while the dashed line shows the model of the background component of fit. (Image: ATLAS Collaboration/CERN).

To separate Higgs-boson events from abundant background processes, ATLAS physicists performed a fit to the distribution of the mass of the reconstructed Z boson and photon. This fit simultaneously determines the number of signal and background events by utilising the different shapes of the signal (narrow peak) and background processes (smooth distribution).

To enhance the sensitivity of the search, physicists separated the potential Higgs-boson events into multiple categories, each with different expected signal-to-background ratios. One of these categories, where the Higgs boson is produced together with two forward jets via the interaction of two weak bosons, used a multivariate discriminant (or “boosted decision tree”) to distinguish it from the other Higgs-boson production modes. Other categories were characterised by the momentum of the photon or the Higgs-boson candidate, or whether the Z boson decayed into electron or muon pairs.

Physicists examined all of these categories simultaneously, studying the distribution of the mass of the reconstructed Z boson and photon in selected events to look for an excess caused by the decays of Higgs bosons to Zγ. Figure 1 shows the Z-boson-plus-photon mass distribution combined over all categories, with the results of the fit overlaid.

A signal yield about twice that expected from the Standard Model, equivalent to a significance of 2.2 standard deviations (5 needed to declare an observation) was found in the data. The result allows ATLAS physicists to exclude, at a 95% confidence level, production rates more than 3.6 larger than what is predicted by the Standard Model. More data are needed to hone in on the Higgs boson decay to Zγ.

Note:

CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 23 Member States.

Links:

- CERN LHC Seminar: Searches for rare and invisible Higgs boson decays and for high-mass resonances with the ATLAS detector by Douglas Michael Schaefer and Takuya Nobe: https://indico.cern.ch/event/868253/

- Searches for the Zγ decay mode of the Higgs boson and for new high-mass resonances in proton-proton collisions at 13 TeV with the ATLAS detector (JHEP 10 (2017) 112, see figures):
https://link.springer.com/article/10.1007%2FJHEP10%282017%29112

- Exploring rare decays of the Higgs boson, Physics Briefing, 11 August 2017:
https://atlas.cern/updates/physics-briefing/exploring-rare-decays-higgs-boson

- See also the full lists of ATLAS Conference Notes and ATLAS Physics Papers:
https://twiki.cern.ch/twiki/bin/view/AtlasPublic/CONFnotes

https://twiki.cern.ch/twiki/bin/view/AtlasPublic/WebHome#Physics_papers

Related links:

Higgs boson: http://atlas.cern/updates/atlas-feature/higgs-boson

ATLAS experiment: https://home.cern/science/experiments/atlas

ATLAS Collaboration: https://atlas.cern/authors/atlas-collaboration

For more information about the European Organization for Nuclear Research (CERN), visit: https://home.web.cern.ch/

Image, Graphic, Text, Credits: CERN/ATLAS Collaboration.

Greetings, Orbiter.ch

For the first time, a spacecraft has returned an aging satellite to service

Northrop Grumman logo.

April 21, 2020

It’s a big step forward for satellite servicing.

View of IS-901 satellite from Mission Extension Vehicle-1’s “near hold” position

In a triumph for the nascent industry of "satellite servicing," an aging communications satellite has returned to service in geostationary orbit.

Northrop Grumman announced Friday that its Mission Extension Vehicle-1, or MEV-1, has restored the Intelsat 901 satellite and relocated it into a position to resume operations.

"We see increased demand for our connectivity services around the world, and preserving our customers’ experience using innovative technology such as MEV-1 is helping us meet that need,” Intelsat Chief Services Officer Mike DeMarco said in a news release.

After launching on a Proton rocket last October, Northrop Grumman's servicing vehicle used its mechanical docking system to latch onto Intelsat 901 on February 25, at an altitude of 36,000km above Earth. Prior to this, no two commercial spacecraft had ever docked in orbit before.

Since then, the MEV-1 servicer has assumed navigation of the combined spacecraft stack, reducing the satellite's inclination by 1.6 degrees and relocating it to a new orbital location, at 332.5° east. Intelsat then transitioned about 30 of its commercial and government customers to the satellite two weeks ago. The transition of service took approximately six hours and was successful.

Based on the agreement between Northrop and Intelsat, MEV-1 will provide five years of life extension services to the satellite before moving it into a graveyard orbit. MEV-1 will then be available to provide additional mission extension services, Northrop said, including orbit raising, inclination corrections, and inspections. Northrop is already building a second MEV to service another Intelsat satellite, 1002, later this year.

MEV-1 Mission with images

This satellite servicing milestone comes as both low-Earth orbit as well as geostationary space—where large, expensive communications satellites are often placed high above the planet to hold their position over the ground—are becoming more crowded. The availability of a service such as that offered by MEV-1 offers satellite providers both the ability to extend the lifetime of aging assets, but also to potentially remove those they have lost control of from the ground.

These kinds of services are generally seen in the space community as important to keeping orbit as decluttered as possible in the coming decades, so it is good that this demonstration case worked out well.

Related links:

Intelsat: http://www.intelsat.com/

Northrop Grumman: https://www.northropgrumman.com/

Image, Video, Text, Credits: Ars Technica/Eric Berger/Northrop Grumman.

Greetings, Orbiter.ch

Exoplanet Apparently Disappears in Latest Hubble Observations

NASA - Hubble Space Telescope patch.

April 20, 2020

Now you see it, now you don't.

What astronomers thought was a planet beyond our solar system has now seemingly vanished from sight. Though this happens in science fiction, such as Superman's home planet Krypton exploding, astronomers are looking for a plausible explanation.

Image above: This artist's illustration depicts the collision of two 125-mile-wide icy, dusty bodies orbiting the bright star Fomalhaut, located 25 light-years away. Image Credits: ESA, NASA and M. Kornmesser.

One interpretation is that, rather than being a full-sized planetary object, which was first photographed in 2004, it could instead be a vast, expanding cloud of dust produced in a collision between two large bodies orbiting the bright nearby star Fomalhaut. Potential follow-up observations might confirm this extraordinary conclusion.

"These collisions are exceedingly rare and so this is a big deal that we actually get to see one," said András Gáspár of the University of Arizona, Tucson. "We believe that we were at the right place at the right time to have witnessed such an unlikely event with NASA's Hubble Space Telescope."

Image above: This diagram simulates what astronomers, studying Hubble Space Telescope observations, taken over several years, consider evidence for the first-ever detection of the aftermath of a titanic planetary collision in another star system. The color-tinted Hubble image on the left is of a vast ring of icy debris encircling the star Fomalhaut, located 25 light-years away. The star is so brilliant that a black occulting disk is used to block out its glare so that the dust ring can be photographed. In 2008, astronomers saw what they thought was the first direct image of a planet orbiting far from the star. However, by 2014, the planet candidate faded below Hubble's detection. The best interpretation is that the object wasn't ever a fully formed planet at all, but an expanding cloud of dust from a collision between two minor bodies, each about 125 miles across. The diagram at the right is based on a simulation of the expanding and fading cloud. The cloud, made of very fine dust particles, is currently estimated to be over 200 million miles across. Smashups like this are estimated to happen around Fomalhaut once every 200,000 years. Therefore, Hubble was looking at the right place at the right time to capture this transient event. Image Credits: NASA, ESA, and A. Gáspár and G. Rieke (University of Arizona).

"The Fomalhaut system is the ultimate test lab for all of our ideas about how exoplanets and star systems evolve," added George Rieke of the University of Arizona's Steward Observatory. "We do have evidence of such collisions in other systems, but none of this magnitude has been observed in our solar system. This is a blueprint of how planets destroy each other."

The object, called Fomalhaut b, was first announced in 2008, based on data taken in 2004 and 2006. It was clearly visible in several years of Hubble observations that revealed it was a moving dot. Until then, evidence for exoplanets had mostly been inferred through indirect detection methods, such as subtle back-and-forth stellar wobbles and shadows from planets passing in front of their stars.

Unlike other directly imaged exoplanets, however, nagging puzzles arose with Fomalhaut b early on. The object was unusually bright in visible light, but did not have any detectable infrared heat signature. Astronomers conjectured that the added brightness came from a huge shell or ring of dust encircling the planet that may possibly have been collision-related. The orbit of Fomalhaut b also appeared unusual, possibly very eccentric.

"Our study, which analyzed all available archival Hubble data on Fomalhaut revealed several characteristics that together paint a picture that the planet-sized object may never have existed in the first place," said Gáspár.

The team emphasizes that the final nail in the coffin came when their data analysis of Hubble images taken in 2014 showed the object had vanished, to their disbelief. Adding to the mystery, earlier images showed the object to continuously fade over time, they say. "Clearly, Fomalhaut b was doing things a bona fide planet should not be doing," said Gáspár.

The interpretation is that Fomalhaut b is slowly expanding from the smashup that blasted a dissipating dust cloud into space. Taking into account all available data, Gáspár and Rieke think the collision occurred not too long prior to the first observations taken in 2004. By now the debris cloud, consisting of dust particles around 1 micron (1/50th the diameter of a human hair), is below Hubble's detection limit. The dust cloud is estimated to have expanded by now to a size larger than the orbit of Earth around our Sun.

Hubble Movie Captures Protoplanetary Collision in the Fomalhaut Star System

Video above: This video simulates what astronomers, studying Hubble Space Telescope observations, consider evidence for the first-ever detection of the aftermath of a titanic planetary collision in another star system. The color-tinted Hubble image on the left is of a vast ring of icy debris encircling the star Fomalhaut, located 25 light-years away. The animated diagram on the right is a simulation of the expanding and fading cloud, based on Hubble observations taken over a period of several years. bVideo Credits: NASA, ESA, and A. Gáspár and G. Rieke (University of Arizona).

Equally confounding is that the team reports that the object is more likely on an escape path, rather than on an elliptical orbit, as expected for planets. This is based on the researchers adding later observations to the trajectory plots from earlier data. "A recently created massive dust cloud, experiencing considerable radiative forces from the central star Fomalhaut, would be placed on such a trajectory," said Gáspár. "Our model is naturally able to explain all independent observable parameters of the system: its expansion rate, its fading and its trajectory."

Because Fomalhaut b is presently inside a vast ring of icy debris encircling the star, colliding bodies would likely be a mixture of ice and dust, like the comets that exist in the Kuiper belt on the outer fringe of our solar system. Gáspár and Rieke estimate that each of these comet-like bodies measured about 125 miles (200 kilometers) across (roughly half the size of the asteroid Vesta).

Hubble Space Telescope (HST). Animation Credits: NASA/ESA

According to the authors, their model explains all the observed characteristics of Fomalhaut b. Sophisticated dust dynamical modeling done on a cluster of computers at the University of Arizona shows that such a model is able to fit quantitatively all the observations. According to the author's calculations, the Fomalhaut system, located about 25 light-years from Earth, may experience one of these events only every 200,000 years.

Gáspár and Rieke — along with other members of an extended team — will also be observing the Fomalhaut system with NASA's upcoming James Webb Space Telescope in its first year of science operations. The team will be directly imaging the inner warm regions of the system, spatially resolving for the first time the elusive asteroid-belt component of an extrasolar planetary system. The team will also search for bona fide planets orbiting Fomalhaut that might be gravitationally sculpting the outer disk. They will also analyze the chemical composition of the disk.

Their paper, "New HST [Hubble] data and modeling reveal a massive planetesimal collision around Fomalhaut" is being published on April 20, 2020, in the Proceedings of the National Academy of Sciences.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

Related links:

Proceedings of the National Academy of Sciences: http://www.pnas.org/

Exoplanets: https://www.nasa.gov/content/the-search-for-life

Hubble Space Telescope (HST): https://www.nasa.gov/mission_pages/hubble/main/index.html

Images (mentioned), Animation (mentioned), Video, Text, Credits: NASA/Rob Garner/GSFC/Claire Andreoli/STSI/Ray Villard/University of Arizona/András Gáspár.

Greetings, Orbiter.ch

Expedition 63 Starts Science, Readies for Cargo and Commercial Crew

ISS - Expedition 63 Mission patch.

April 20, 2020

The three-member Expedition 63 crew is beginning its first full workweek and kicking off science aboard the International Space Station. More space traffic continues this week, as Russia gets ready to launch its next Progress resupply ship late Friday.

NASA astronaut Chris Cassidy is on his third spaceflight and is in command of the orbiting lab. His two crewmates, Roscosmos cosmonauts Anatoly Ivanishin and Ivan Vagner, will be with Cassidy until October.

Image above: NASA astronauts (from left) Chris Cassidy and Andrew Morgan pose for a portrait inside the Quest airlock. Cassidy is a U.S. Navy SEAL and Captain. Morgan is an emergency physician and Colonel in the U.S. Army. Morgan returned to Earth on April 17. Image Credit: NASA.

Cassidy worked Monday on physics research checking out the Electrostatic Levitation Furnace in the Japanese Kibo laboratory module. The experiment facility heats samples to ultra-high temperatures to observe thermophysical properties difficult to measure in Earth’s gravity.

Ivanishin and Vagner are getting ready for the arrival of a new space shipment due to arrive on Saturday at 1:23 a.m. EDT aboard the Progress 75 (75P) resupply ship. The 75P will launch Friday at 9:51 p.m. and take two orbits around the Earth before automatically docking to the rear port of the Zvezda service module. The duo tested a device on Monday that can remotely maneuver the 75P to a docking if necessary.

International Space Station (ISS). Animation Credit: NASA

The two cosmonauts also collaborated on a variety of Russian space research throughout Monday. The pair looked at microgravity’s effect on pain sensitivity and bone tissue. During the afternoon, they explored how future space travelers may pilot spacecraft on planetary missions.

NASA and SpaceX announced May 27 for the first launch of humans from the United States since 2011. NASA astronauts Robert Behnken and Doug Hurley will lift off at 4:23 p.m. from Florida aboard the Crew Dragon spacecraft and test its systems. They will join the Expedition 63 crew a day later after docking to the forward port of the station’s Harmony module.

Related links:

Expedition 63: https://www.nasa.gov/mission_pages/station/expeditions/expedition63/index.html

Electrostatic Levitation Furnace: https://www.nasa.gov/mission_pages/station/research/experiments/explorer/Facility.html?#id=1536

Kibo laboratory module: https://www.nasa.gov/mission_pages/station/structure/elements/japan-kibo-laboratory

Zvezda service module: https://www.nasa.gov/mission_pages/station/structure/elements/zvezda-service-module.html

Bone tissue: https://www.energia.ru/en/iss/researches/human/21.html

Pain sensitivity: https://www.energia.ru/en/iss/researches/human/17.html

Pilot spacecraft: https://www.energia.ru/en/iss/researches/human/24.html

Harmony module: https://www.nasa.gov/mission_pages/station/structure/elements/harmony

Space Station Research and Technology: https://www.nasa.gov/mission_pages/station/research/index.html

International Space Station (ISS): https://www.nasa.gov/mission_pages/station/main/index.html

Image (mentioned), Animation (mentioned), Text, Credits: NASA/Mark Garcia.

Best regards, Orbiter.ch

EPFL takes part in a giant telescope project

EPFL - École Polytechnique Fédérale de Lausanne logo.

April 20, 2020

EPFL will be responsible for coordinating the contributions of the Swiss scientific community to this project involving thirteen countries.

Image above: The Square Kilometer Array (SKA) is designed to detect radio waves from celestial objects. (Photo: EPFL).

EPFL will participate in the construction of the largest radio telescope ever developed. Called “Square Kilometer Array” (SKA), the project involves thirteen countries and is intended to unravel certain mysteries of the universe.
Video Amazing new images of the Sun’s surface

This giant telescope is one of the "most ambitious scientific tools of the 21st century," said the Federal Polytechnic of Lausanne (EPFL) on Monday in a press release. She explains that she has acceded to the organizing committee and that she will be responsible for coordinating the contributions of the Swiss scientific community to the project.

Image above: The Square Kilometer Array (SKA) is designed to detect radio waves from celestial objects. (Photo: SKA/Wikimedia).

The SKA will be built over the next few years on two sites: in South Africa with 130 antennas 15 meters in diameter and in Austalia with 130,000 parabolic-type antennas. "Thanks to this installation, some of the great mysteries of the universe will be able to be studied in detail," promises EPFL.

Radio waves

The SKA is designed to detect radio waves emanating from celestial objects, the same type of emissions used for example by smartphones. It is thus distinguished from most telescopes which are based on visible light.

"This new high performance telescope will give us a new vision of the universe," notes Jean-Paul Kneib, director of the Astrophysics Laboratory at EPFL. "The SKA can for example identify planetary systems in formation, galaxies surrounded by hydrogen gas, or even black holes present in the center of galaxies located billions of light years away," he explains, quoted in the press release.

EPFL joins the giant radio telescope SKA for the Swiss community

The SKA organizing committee, of which EPFL is now a member, must oversee the design of the telescope until the transition to international observatory is completed. This should take place during 2020.

EPFL then Switzerland

EPFL membership should benefit "the entire Swiss scientific community and will open up new perspectives for companies," notes Xavier Reymond, director of the International Research Organizations sector of the State Secretariat for Education.

After EPFL, Switzerland could become a full member of the SKA organizing committee. A first debate has been launched recently in the Parliament, underlines the Lausanne university.

EPFL campus in Switzerland. Banner Credit: EPFL

Several members of the Swiss academic community are involved in the project, under the aegis of EPFL. These include the Universities of Geneva, Zurich and Bern, the EPFZ in Zurich, the Swiss National Supercomputing Center (CSCS), the University of Applied Sciences of North-West Switzerland (FHNW) or the Planetarium of the Museum Lucernre transport.

École Polytechnique Fédérale de Lausanne - Federal Institute of Technology from Lausanne (EPFL): https://www.epfl.ch/en/

Images (mentioned), Text, Video, Text, Credits: ATS/EPFL/Orbiter.ch Aerospace/Roland Berga.

Best regards, Orbiter.ch

Interstellar Comet Borisov Reveals Its Chemistry and Possible Origins

NASA - Hubble Space Telescope patch / ALMA - Atacama Large Millimeter/submillimeter Array logo.

April 20, 2020

On Aug. 30, 2019, when amateur astronomer Gennady Borisov gazed upward with his homemade telescope, he spotted an object moving in an unusual direction. Now called 2I/Borisov, this runaway point of light turned out to be the first confirmed comet to enter our solar system from some unknown place beyond our Sun’s influence. Astronomers everywhere rushed to take a look with some of the most powerful instruments in the world, hoping to learn as much as they could about the mysterious visitor.

Now, thanks to observations with NASA’s Hubble Space Telescope and the National Radio Astronomy Observatory’s Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have figured out that 2I/Borisov has an unusual composition. Specifically, it has a higher concentration of carbon monoxide than any comet seen at a similar distance; that is, within about 200 million miles (300 million kilometers) of the Sun.

Hubble Space Telescope (HST). Animation Credits: ESA/NASA

This suggests to scientists that the comet could have formed around a red dwarf — a smaller, fainter type of star than the Sun — though other kinds of stars are possible. Another idea is that 2I/Borisov could be a carbon monoxide-rich fragment of a small planet.

What is an interstellar comet?

Comets are snowballs of ice, dust and frozen gas. When totally frozen (or “inactive”), they’re approximately the diameter of a small town, but when heated by the Sun their tails can extend for millions of miles. 2I/Borisov is about the length of nine football fields, or 0.61 miles (0.98 kilometers), making it relatively small. The new results on the comet’s composition are published in the journal Nature Astronomy.

All comets form in the primordial disk of material that encircles a young star, preserving remnants of a planetary system’s ancient past. Comets from our own solar neighborhood reveal the history of materials, including water, that made Earth the planet we know today, as well as our other planetary neighbors. An interstellar comet, on the other hand, is a chemical ambassador from an entirely different star system — containing a treasure trove of clues to worlds too far to reach with modern technology.

“With an interstellar comet passing through our own solar system, it’s like we get a sample of a planet orbiting another star showing up in our own backyard,” said John Noonan of the Lunar and Planetary Laboratory at the University of Arizona, Tucson, and a member of the Hubble research team led by Dennis Bodewits of Auburn University in Alabama.

What scientists found

Bodewits and colleagues used Hubble to look at 2I/Borisov from Dec. 11, 2019 to Jan. 13, 2020. Separately, a team of international scientists led by Martin Cordiner and Stefanie Milam at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, studied the comet on December 15 and 16, 2019, with ALMA, an array of radio telescopes at an altitude of 16,570 feet (5,050 meters) in northern Chile. Radio telescopes are especially useful for looking at cold, low-energy gas in objects like comets.

Results from both Hubble and ALMA estimate that 2I/Borisov’s carbon monoxide concentration is higher than that of the average solar system comet. 

Animation above: This is a time-lapse sequence compressing Hubble Space Telescope observations of comet 2I/Borisov, spanning a seven-hour period. As the second known interstellar object to enter our solar system, the comet is moving along at a breakneck speed of 110,000 miles per hour (180,000 kilometers per hour). To photograph the comet Hubble has to track it, like a photographer tracking a racetrack horse. Therefore, background stars are streaked in the exposure frames. An artificial satellite also crosses the field of view. Hubble reveals a central concentration of dust around an unseen nucleus. Comet 2I/Borisov is only the second such interstellar object known to have passed through the solar system. In 2017, the first identified interstellar visitor, an object formally named 'Oumuamua', swung within 24 million miles (39 million kilometers) of the Sun before racing out of the solar system. Image Credits: NASA, ESA and J. DePasquale (STScI).

Where did it come from?

A high carbon-monoxide-to-water ratio suggests that the comet has traveled from a very cold place — as cold as the area where Pluto is in relation to our Sun, called the Kuiper Belt. The group using Hubble additionally theorizes 2I/Borisov may have originated around the most common type of star in the Milky Way: a red dwarf. Red dwarfs are much smaller and dimmer than the Sun, so the planet-forming material around them would be colder than the building blocks of our solar system.

“These stars have exactly the low temperatures and luminosities where a comet could form with the type of composition found in comet 2I/Borisov,” said Noonan.

Scientists using ALMA say it’s possible that 2I/Borisov could be a fragment of a dwarf planet that had a lot of carbon monoxide near its surface, regardless of which type of star it came from. “If that object collided with another, then the carbon monoxide-rich fragments could be released into space,” said Cordiner.

But 2I/Borisov may have simply formed as a comet with a high concentration of carbon monoxide, the ALMA team points out. Alternatively, it may have an unusually thick outer layer that insulates frozen gases like hydrogen cyanide and water. As the more volatile carbon monoxide evaporates or “outgasses,” it may appear more abundant than other cometary gases. 2I/Borisov’s unusual properties may also suggest a wider diversity of carbon monoxide in comets in our own solar system than previously thought.

“Whatever the answer is, 2I/Borisov opens up a whole new can of worms for cometary science,” says Milam, one of the scientists using ALMA.

 ALMA - Atacama Large Millimeter/submillimeter Array telescope. Image Credit: ESO

In our own solar system, there are two places where most comets reside: The Kuiper Belt, an area that includes Pluto; and the Oort Cloud, which is much farther away. All of these comets likely formed closer to the Sun, but may have been booted outward by the erratic movements of Jupiter and Saturn billions of years ago. These giant planets, because of their immense gravity, could have even sent comets flying toward other stars, escaping the influence of the Sun’s gravity altogether.

Given this history, scientists using Hubble theorize that a massive planet in a red dwarf system, in an environment with frozen carbon monoxide, may have punted 2I/Borisov our way.

“If a Jupiter-sized planet migrates inward, it could kick out a lot of these comets,” Bodewits said.

The team using ALMA agrees that a young moving planet likely sent the comet on its way. “Then, after a cold, lonely voyage, 2I/Borisov made its close encounter with our solar system and started outgassing and showing us what it’s got inside,” Cordiner says.

More to come

2I/Borisov is only the second object astronomers have detected that definitely came from a different star system. The first was 'Oumuamua, discovered in October 2017, that whizzed by too quickly for scientists to pin down its chemistry. Whether it too is a comet, an asteroid, or something else — we may never know.

2I/Borisov is continuing on its path through the solar system, and will eventually head out. As more advanced telescopes and other instruments turn on and gaze out in the coming years, astronomers expect to find more interstellar objects, though they will still be rare.

“Our solar system is so tiny compared to the distances between star systems,” Cordiner says. “For an interstellar comet to come in and hit the bullseye like Borisov did is incredible.”

Related links:

NASA’s Hubble Space Telescope (HST): https://www.nasa.gov/hubble

National Radio Astronomy Observatory’s Atacama Large Millimeter/submillimeter Array (ALMA): https://www.almaobservatory.org/en/home/

Comets: https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/overview/

NASA/Tricia Talbert/Written by Elizabeth Landau.

Ending global plant tracking, Proba-V assigned new focus

ESA - Proba-V Mission logo.

April 20, 2020

Proba-V global vegetation timelapse

ESA’s cubic-metre-sized Proba-V minisatellite will soon end its nearly seven-year global mission to monitor the daily growth of all Earth’s vegetation. As Copernicus Sentinel-3 takes on this task instead, Proba-V will be free to perform experimental monitoring over Europe and Africa – including co-observations with new companion missions.

Despite its small size, Proba-V maintains a continent-spanning perspective: its main Vegetation imager has a 2250-km wide swath. This enables it to cover nearly the entire vegetated surface of the globe every day. Allowing for cloud cover, the mission builds up a complete snapshot of global plant growth every 10 days. Overall, the mission has acquired more than a petabyte of environmental data during its time in orbit.

Proba-V satellite

Proba-V's extremely wide view comes about because Vegetation is made up of three separate imaging telescopes, possessing 300 m spatial resolution, which rises to 100 m resolution in the central telescope – a marked improvement on the previous generation of Vegetation instruments.

“Proba-V began as a ‘gap-filler’ mission to ensure data coverage between the Vegetation instruments flown on the full-sized Spot-4 and -5 satellites and Copernicus Sentinel-3,” explains ESA Earth Observation operations manager Roberto Biasutti.

Vegetation swath

“It started with a two-year mission lifetime, which was repeatedly extended, and the satellite remains in excellent overall health. So even though its global mission is due to end this June, shortly after its seventh birthday, the plan is to let it go on working.”

Proba-V was launched into what is called a ‘Sun-synchronous’ orbit, where it keeps pace with the Sun as it circles Earth at 820 km altitude, allowing it the maximum possible observing daylight. This orbit is gradually decaying however, and the minisatellite lacks onboard thrusters to correct it. Tugged by the gravitational pull of Earth’s equatorial bulge, its observing time is gradually growing earlier in the local morning.

 Vegetation instrument

“Basically one of the cameras on Proba-V will soon be observing night-time rather than daylight, meaning it cannot go on delivering daily global coverage anymore to continue the 20 year plus Vegetation time series, so its operational global mission has to end,” comments Dennis Clarijs of VITO, the Belgian research and service centre processing and distributing Proba-V data to users.

“But this isn’t the end of the mission. Instead ESA will be applying its excellent geometric and radiometric performance to make test observations in Europe and Africa, particularly the African Sahel where its results help provide early drought warnings.

Proba-V monitors African Sahel

“This means the more than 1800 research teams making use of Proba-V data today still have more data to look forward to, albeit on an experimental rather than operational basis. This is good because its 100-m imagery fills a particular niche, as a midway step between Copernicus Sentinel-2 and -3, able to resolve individual field delineations in some cases. Proba-V’s 100-m imagery is also routinely used to cross-check other products, such as the Copernicus Global Land Service.”

Proba-V will also be increasing its observations of the Moon. It is not generally known, but many Earth observation satellites routinely observe our planet’s natural satellite along with Earth itself: the unchanging state of the lunar surface makes it an excellent calibration target.

The Moon seen by ESA's Proba-V

In the past Proba-V made such lunar acquisitions on a monthly basis. Now the minisatellite will increase them, experimenting with changing frequencies and view angles for the benefit of future Earth-observing missions.

In addition, the plan is to launch in 2021 an additional tiny satellite carrying a single telescope version of the same Vegetation imager aboard Proba-V.

Proba-V shown with Sentinel-3

Roberto comments: “This companion mission is currently being developed by Belgian startup Aerospace Lab for launch next year. Based on a tiny 12-unit CubeSat  - built up from standardised 10 cm cubic units –  it will image  the same targets as Proba-V areas at the same time except from a different viewing angle, allowing the creation of combined ‘fusion’ image products.

“A major motive behind the original Proba-V mission was to see if an instrument previously hosted on a full-sized satellite could do good work from a smaller platform. With this companion satellite we will raise the bar, using an even smaller, cheaper platform.”

Changing Nile Delta seen by Proba-V

Another companion satellite is also being planned, to host either a thermal infrared imager or an hyperspectral instrument, both of which would offer valuable synergies with Vegetation observations, and test the feasibility of small satellite constellations entering operations in future.

Proba-V’s orbital decay will finally bring it into complete darkness in October 2021, when it will either be shut down, or placed in suspended animation, awaiting a time when its orbit brings it into daylight again.

“There is a precedent for such an arrangement,” adds Roberto, “with predecessor mission Proba-1, launched back in 2001, hosting a hyperspectral camera. Having passed through such a period of orbital darkness it is still observing to this day.”

Related links:

Proba Missions: http://www.esa.int/Enabling_Support/Space_Engineering_Technology/Proba_Missions

Proba-V: http://www.esa.int/Applications/Observing_the_Earth/Proba-V

VITO: https://vito.be/en

Copernicus Sentinel-3: https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-3

Images, Animations, Text, Credits: ESA/P.Carril/VITO/Terrascope/CNES/QinetiQ Space/Belspo – produced by VITO.

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