Category Archives: Exoplanets

Astronomy, Exoplanets, Space Science, Space sciences roundup

Space sciences roundup – Jan.29.2020

A sampling of recent articles, videos, and images from space-related science news items (find previous roundups here):

Astronomy

** What Does a Black Hole Look Like: How We Got Our First Picture –  Dr. Eliot Quataert of the University of California, Berkeley gave this recent Silicon Valley Astronomy Lecture:

Black holes are one of the most remarkable predictions of Einstein’s theory of gravity: so much material is compressed into such a small volume that nothing, not even light, can escape. In Spring 2019, the world-wide Event Horizon Telescope released the first real picture of gas around a massive black hole and the “shadow” it makes as the gas swirls into the black hole. Dr. Quataert describes how these pioneering observations were made and what they have taught us about black

** NASA’s Kepler Witnesses Vampire Star System Undergoing Super-Outburst | NASA

NASA’s Kepler spacecraft was designed to find exoplanets by looking for stars that dim as a planet crosses the star’s face. Fortuitously, the same design makes it ideal for spotting other astronomical transients – objects that brighten or dim over time. A new search of Kepler archival data has uncovered an unusual super-outburst from a previously unknown dwarf nova. The system brightened by a factor of 1,600 over less than a day before slowly fading away.

The star system in question consists of a white dwarf star with a brown dwarf companion about one-tenth as massive as the white dwarf. A white dwarf is the leftover core of an aging Sun-like star and contains about a Sun’s worth of material in a globe the size of Earth. A brown dwarf is an object with a mass between 10 and 80 Jupiters that is too small to undergo nuclear fusion.

The brown dwarf circles the white dwarf star every 83 minutes at a distance of only 250,000 miles (400,000 km) – about the distance from Earth to the Moon. They are so close that the white dwarf’s strong gravity strips material from the brown dwarf, sucking its essence away like a vampire. The stripped material forms a disk as it spirals toward the white dwarf (known as an accretion disk).

“This illustration shows a newly discovered dwarf nova system, in which a white dwarf star is pulling material off a brown dwarf companion. The material collects into an accretion disk until reaching a tipping point, causing it to suddenly increase in brightness. Using archival Kepler data, a team observed a previously unseen, and unexplained, gradual intensification followed by a super-outburst in which the system brightened by a factor of 1,600 over less than a day. Credits: NASA and L. Hustak (STScI)“

It was sheer chance that Kepler was looking in the right direction when this system underwent a super-outburst, brightening by more than 1,000 times. In fact, Kepler was the only instrument that could have witnessed it, since the system was too close to the Sun from Earth’s point of view at the time. Kepler’s rapid cadence of observations, taking data every 30 minutes, was crucial for catching every detail of the outburst.

The event remained hidden in Kepler’s archive until identified by a team led by Ryan Ridden-Harper of the Space Telescope Science Institute (STScI), Baltimore, Maryland, and the Australian National University, Canberra, Australia. “In a sense, we discovered this system accidentally. We weren’t specifically looking for a super-outburst. We were looking for any sort of transient,” said Ridden-Harper.

Kepler captured the entire event, observing a slow rise in brightness followed by a rapid intensification. While the sudden brightening is predicted by theories, the cause of the slow start remains a mystery. Standard theories of accretion disk physics don’t predict this phenomenon, which has subsequently been observed in two other dwarf nova super-outbursts.

Exoplanets

** The Space Show – Tue, 01/21/2020 – Dr. Jeffrey Coughlin talked about “Exoplanets, the search for life, five exoplanet detection methods, exoplanet atmosphere biosignature detection and more”.

** NASA Planet Hunter Finds its 1st Earth-size Habitable-zone World – NASA

NASA’s Transiting Exoplanet Survey Satellite (TESS) has discovered its first Earth-size planet in its star’s habitable zone, the range of distances where conditions may be just right to allow the presence of liquid water on the surface. Scientists confirmed the find, called TOI 700 d, using NASA’s Spitzer Space Telescope and have modeled the planet’s potential environments to help inform future observations.

TOI 700 d is one of only a few Earth-size planets discovered in a star’s habitable zone so far. Others include several planets in the TRAPPIST-1 system and other worlds discovered by NASA’s Kepler Space Telescope.

“TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars,” said Paul Hertz, astrophysics division director at NASA Headquarters in Washington. “Planets around nearby stars are easiest to follow-up with larger telescopes in space and on Earth. Discovering TOI 700 d is a key science finding for TESS. Confirming the planet’s size and habitable zone status with Spitzer is another win for Spitzer as it approaches the end of science operations this January.”

** TESS Discovers Its 1st Planet Orbiting 2 Stars – NASA

In 2019, when Wolf Cukier finished his junior year at Scarsdale High School in New York, he joined NASA’s Goddard Space Flight Center in Greenbelt, Maryland, as a summer intern. His job was to examine variations in star brightness captured by NASA’s Transiting Exoplanet Survey Satellite (TESS) and uploaded to the Planet Hunters TESS citizen science project.

“I was looking through the data for everything the volunteers had flagged as an eclipsing binary, a system where two stars circle around each other and from our view eclipse each other every orbit,” Cukier said. “About three days into my internship, I saw a signal from a system called TOI 1338. At first I thought it was a stellar eclipse, but the timing was wrong. It turned out to be a planet.”

A SETI Institute view on the TESS findings:

Interstellar space

** Voyager 2, 18.5 billion kilometers from earth, recovers after power glitch: Voyager 2 Engineers Working to Restore Normal Operations – NASA JPL

Engineers for NASA’s Voyager 2 spacecraft are working to return the mission to normal operating conditions after one of the spacecraft’s autonomous fault protection routines was triggered. Multiple fault protection routines were programmed into both Voyager 1 and Voyager 2 in order to allow the spacecraft to automatically take actions to protect themselves if potentially harmful circumstances arise. At NASA’s Jet Propulsion Laboratory in Pasadena, California, engineers are still communicating with the spacecraft and receiving telemetry.

Launched in 1977, Voyager 1 and Voyager 2 are both in interstellar space, making them the most distant human-made objects in the solar system. On Saturday, Jan. 25, Voyager 2 didn’t execute a scheduled maneuver in which the spacecraft rotates 360 degrees in order to calibrate its onboard magnetic field instrument. Analysis of the telemetry from the spacecraft indicated that an unexplained delay in the onboard execution of the maneuver commands inadvertently left two systems that consume relatively high levels of power operating at the same time. This caused the spacecraft to overdraw its available power supply.

It’s a long way to make a service call:

It has taken the team several days to assess the current situation primarily because of Voyager 2’s distance from Earth – about 11.5 billion miles (18.5 billion kilometers). Communications traveling at the speed of light take about 17 hours to reach the spacecraft, and it takes another 17 hours for a response from the spacecraft to return to Earth. As a result, mission engineers have to wait about 34 hours to find out if their commands have had the desired effect on the spacecraft.

Voyager 1 Entering Interstellar Space (Artist Concept)
“This artist’s concept depicts one of NASA’s Voyager spacecraft entering interstellar space, or the space between stars. Interstellar space is dominated by the plasma, or ionized gas, that was ejected by the death of nearby giant stars millions of years ago.” Credit: NASA/JPL-Caltech

Sun

** An update on activity on the Sun’s surface: Sunspot update: The record flatline continues | Behind The Black

In the month of December 2019 the Sun continued its longest stretch of overall sunspot inactivity ever recorded, reaching seven months in length. At no point since the last grand minimum in the 1600s have scientists ever seen so few sunspots over so long a time period.
…

December saw only two sunspots, both becoming active on the same day, December 24. Both also had a polarity belonging to the next solar cycle, providing evidence that we will have another sunspot maximum sometime in the next five years, and that we are not heading to another grand minimum where there are no sunspots for decades.

See SpaceWeather.com for daily updates on sunspots.

** Parker Solar Probe sets new record for spacecraft nearness to the Sun: Parker Solar Probe Completes Fourth Closest Approach, Breaks New Speed and Distance Records – Parker Solar Probe/NASA

At 4:37 a.m. EST on Jan. 29, 2020, NASA’s Parker Solar Probe broke speed and distance records as it completed its fourth close approach of the Sun. The spacecraft traveled 11.6 million miles from the Sun’s surface at perihelion, reaching a speed of 244,225 miles per hour. These achievements topple Parker Solar Probe’s own previous records for closest spacecraft to the Sun — previously about 15 million miles from the Sun’s surface — and fastest human-made object, before roughly 213,200 miles per hour.

Parker Solar Probe will continue to fly ever closer to the Sun on its seven-year journey, exploring regions of space never visited before and providing scientists with key measurements to help unveil the mysteries of the solar corona and wind.

As with most of Parker Solar Probe’s close approaches, the spacecraft is out of contact with Earth for several days around perihelion.

Listen to the sounds of the Sun as recorded by the probe: Parker Solar Probe Team Hears First Whispers of the Solar Wind’s Birth – JHU-APL

There’s a wind that emanates from the Sun. It blows not like a soft whistle but like a hurricane’s scream. Made of electrons, protons and heavier ions, the solar wind courses through the solar system at roughly 1 million mph (1.6 million kph), barreling over everything in its path. Yet through the wind’s roar, NASA’s Parker Solar Probe hears the small chirps, squeaks and rustles that hint at the origin of this mysterious and ever-present wind. The spacecraft’s FIELDS instrument can eavesdrop on the electric and magnetic fluctuations caused by plasma waves. The Parker Solar Probe it can “hear” when the waves and particles interact with one another, recording frequency and amplitude information about these plasma waves that scientists could then play as sound waves. And it results in some striking sounds. Solar wind sounds playlist: https://soundcloud.com/jhu-apl/sets/s…

Jupiter

** Mighty Jupiter Revealed | The Planetary Society

It’s more massive than all the other planets combined. In nearly four years at Jupiter the Juno spacecraft has returned science that is revolutionizing our understanding of this gigantic world. Principal investigator Scott Bolton shows us the mysterious cyclones at its poles and that famously persistent red spot. Casey Dreier says the United States House of Representatives has proposed legislation that is at odds with NASA’s current Moon and Mars plans. John Flamsteed almost discovered Uranus! Bruce Betts will tell us where he went wrong in this week’s What’s Up space trivia contest.

[ Update: Juno flyby video created by citizen scientist Brian Swift (via Bob Zimmerman):

]

 

Moon

** China releases data and imagery from Chang’e 4 mission to the Moon’s far side:

Chinese officials marked the one-year anniversary of the Chang’e 4 mission’s historic first soft landing on the far side of the moon [January 3rd] with the public release of data collected by scientific instruments and cameras on the lunar lander and rover.

The Chang’e 4 lander and Yutu 2 rover landed together on the lunar surface Jan. 3, 2019, marking the first time a spacecraft has ever safely touched down on the far side of the moon.

Around 12 hours after touchdown, the Yutu 2 rover drove down a ramp to disembark from the Chang’e 4 mission’s stationary landing platform to begin exploring the barren lunar landscape.

Scientific instruments and cameras aboard the Chang’e 4 lander and Yutu 2 rover have downlinked measurements and numerous images in the past year. The Chang’e 4 mission relays data through a dedicated Chinese communications satellite positioned beyond the far side of the moon, with a line of sight to both Chang’e 4 and Earth-based receiving stations.

On Friday, the one-year anniversary of the mission’s successful landing, China National Space Administration and the Chinese Academy of Sciences published scientific data collected by five instruments on the Chang’e 4 lander and Yutu 2 rover.

China’s Yutu-2 rover on the Moon.

Asteroids

** In December the OSIRIS-REx team selected a spot for sample-taking on asteroid Bennu. Next August, the spacecraft will land briefly and grab a sample of regolith to return to Earth in 2023: X Marks the Spot: NASA Selects Site for Asteroid Sample Collection – OSIRIS-REx Mission

After a year scoping out asteroid Bennu’s boulder-scattered surface, the team leading NASA’s first asteroid sample return mission has officially selected a sample collection site.

The Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-Rex) mission team concluded a site designated “Nightingale” – located in a crater high in Bennu’s northern hemisphere – is the best spot for the OSIRIS-REx spacecraft to snag its sample.

The OSIRIS-REx team spent the past several months evaluating close-range data from four candidate sites in order to identify the best option for the sample collection. The candidate sites – dubbed Sandpiper, Osprey, Kingfisher, and Nightingale – were chosen for investigation because, of all the potential sampling regions on Bennu, these areas pose the fewest hazards to the spacecraft’s safety while still providing the opportunity for great samples to be gathered.

“This flat projection mosaic of asteroid Bennu shows the relative locations of the primary and backup sample collection sites on the asteroid: Nightingale and Osprey. NASA’s OSIRIS-REx spacecraft is scheduled to collect a sample in summer 2020.” Credit: NASA/Goddard/University of Arizona

This month the spacecraft made a low pass over the Nightingale spot to inspect it further: OSIRIS-REx Completes Closest Flyover of Sample Site Nightingale – OSIRIS-REx Mission

Preliminary results indicate that NASA’s OSIRIS-REx spacecraft successfully executed a 0.4-mile (620-m) flyover of site Nightingale yesterday as part of the mission’s Reconnaissance B phase activities. Nightingale, OSIRIS-REx’s primary sample collection site, is located within a crater high in asteroid Bennu’s northern hemisphere.

To perform the pass, the spacecraft left its 0.75-mile (1.2-km) safe home orbit and flew an almost 11-hour transit over the asteroid, aiming its science instruments toward the 52-ft (16-m) wide sample site before returning to orbit. Science observations from this flyover are the closest taken of a sample site to date.

The primary goal of the Nightingale flyover was to collect the high-resolution imagery required to complete the spacecraft’s Natural Feature Tracking image catalog, which will document the sample collection site’s surface features – such as boulders and craters. During the sampling event, which is scheduled for late August, the spacecraft will use this catalog to navigate with respect to Bennu’s surface features, allowing it to autonomously predict where on the sample site it will make contact . Several of the spacecraft’s other instruments also took observations of the Nightingale site during the flyover event, including the OSIRIS-REx Thermal Emissions Spectrometer (OTES), the OSIRIS-REx Visual and InfraRed Spectrometer (OVIRS), the OSIRIS-REx Laser Altimeter (OLA), and the MapCam color imager.

Mars

** The European Mars Express views the northern ice cap: Rippling ice and storms at Mars’ north pole – ESA

Mars’ north polar ice cap in 3D: “This image shows shows part of the ice cap at Mars’ north pole in 3D when viewed using red-green or red-blue glasses. This anaglyph was derived from data obtained by the nadir and stereo channels of the High Resolution Stereo Camera (HRSC) on ESA’s Mars Express during spacecraft orbit 3670. It covers a part of the martian surface centred at about 244°E/85°N. North is to the upper right.” Credits: ESA

** Updates on Curiosity‘s roving from Leonard David:

“Curiosity Left B Navigation Camera image taken on Sol 2659, January 29, 2020. Credit: NASA/JPL-Caltech” via Leonard David

** More of the marvelous Martian surface – Bob Zimmerman

“Convergent and Overlapping Narrow Curved Ridges” in the Martian mid-latitudes, taken by the HiRISE camera on the Mars Reconnaissance Orbiter (MRO) and here  cropped and rotated by Bob Zimmerman

** Insight‘s mole digs in reverse again:

** China to launch an Mars orbiter and rover mission in July on a Long March 5 heavy lift rocket.

The Chinese combination Mars orbiter, lander, and rover is shown here in tests for launching. Credits: China Aerospace Technology Corporation

NASA’s Mars 2020 mission aims to launch during a window between July 17 – Aug. 5, 2020 and land on Feb. 18, 2021. The rover is of a similar design to that of Curiosity, which landed on Mars on August 5, 2012. The Mars 2020 rover will soon get a name as well: Nine Finalists Chosen in NASA’s Mars 2020 Rover Naming Contest – NASA’s Mars Exploration Program.

The joint European/Russian ExoMars 2020 mission aims to launch on a Russian Proton rocket this summer and land on Mars on March 19, 2021. Problems with the parachutes need to be resolved else the mission will have to wait another two years for the next launch window: Promising progress for ExoMars parachutes – ESA

Artist’s view of the ESA Exomars rover on Mars.

 

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The Planet Factory:
Exoplanets and the Search for a Second Earth

Astronomy, Education, Exoplanets

Video: An overview of finding and studying exoplanets

Dr. Courtney Dressing of the University of California at Berkeley gives a public lecture on exoplanets:

The NASA Kepler mission revealed that our Galaxy is teeming with planetary systems and that Earth-sized planets are common. However, most of the planets detected by Kepler orbit stars too faint to permit detailed study. The NASA Transiting Exoplanet Survey Satellite (TESS,) launched in 2018, is now finding hundreds of small planets orbiting stars that are much closer and brighter. Dr. Dressing discusses how we find exoplanets, describes the TESS mission, and explains how it (and future projects) will help our understanding of what planets are out there and how they form.

The lecture is one in the Silicon Valley Astronomy Lectures  series organized and moderated by Foothill’s astronomy instructor Andrew Fraknoi and jointly sponsored by the Foothill College Astronomy Department, NASA’s Ames Research Center, the SETI Institute, and the Astronomical Society of the Pacific.

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The Planet Factory: Exoplanets and the Search for a Second Earth

Astronomy, Exoplanets

ESO: First Giant Planet around White Dwarf Found

The latest news from the European Southern Observatory (ESO):

First Giant Planet around White Dwarf Found
ESO observations indicate the Neptune-like exoplanet is evaporating

This illustration shows the white dwarf WDJ0914+1914 and its Neptune-like exoplanet. Since the icy giant orbits the hot white dwarf at close range, the extreme ultraviolet radiation from the star strips away the planet’s atmosphere. While most of this stripped gas escapes, some of it swirls into a disc, itself accreting onto the white dwarf.

Researchers using ESO’s Very Large Telescope [VLT] have, for the first time, found evidence of a giant planet associated with a white dwarf star. The planet orbits the hot white dwarf, the remnant of a Sun-like star, at close range, causing its atmosphere to be stripped away and form a disc of gas around the star. This unique system hints at what our own Solar System might look like in the distant future.

“It was one of those chance discoveries,”

says researcher Boris Gänsicke, from the University of Warwick in the UK, who led the study, published today in Nature.

The team had inspected around 7000 white dwarfs observed by the Sloan Digital Sky Survey and found one to be unlike any other. By analysing subtle variations in the light from the star, they found traces of chemical elements in amounts that scientists had never before observed at a white dwarf.

“We knew that there had to be something exceptional going on in this system, and speculated that it may be related to some type of planetary remnant.” 

To get a better idea of the properties of this unusual star, named WDJ0914+1914, the team analysed it with the X-shooter instrument on ESO’s Very Large Telescope in the Chilean Atacama Desert. These follow-up observations confirmed the presence of hydrogen, oxygen and sulphur associated with the white dwarf. By studying the fine details in the spectra taken by ESO’s X-shooter, the team discovered that these elements were in a disc of gas swirling into the white dwarf, and not coming from the star itself.

“It took a few weeks of very hard thinking to figure out that the only way to make such a disc is the evaporation of a giant planet,”

says Matthias Schreiber from the University of Valparaiso in Chile, who computed the past and future evolution of this system.

The detected amounts of hydrogen, oxygen and sulphur are similar to those found in the deep atmospheric layers of icy, giant planets like Neptune and Uranus. If such a planet were orbiting close to a hot white dwarf, the extreme ultraviolet radiation from the star would strip away its outer layers and some of this stripped gas would swirl into a disc, itself accreting onto the white dwarf. This is what scientists think they are seeing around WDJ0914+1914: the first evaporating planet orbiting a white dwarf.

Combining observational data with theoretical models, the team of astronomers from the UK, Chile and Germany were able to paint a clearer image of this unique system. The white dwarf is small and, at a blistering 28 000 degrees Celsius (five times the Sun’s temperature), extremely hot. By contrast, the planet is icy and large—at least twice as large as the star. Since it orbits the hot white dwarf at close range, making its way around it in just 10 days, the high-energy photons from the star are gradually blowing away the planet’s atmosphere. Most of the gas escapes, but some is pulled into a disc swirling into the star at a rate of 3000 tonnes per second. It is this disc that makes the otherwise hidden Neptune-like planet visible.

“This is the first time we can measure the amounts of gases like oxygen and sulphur in the disc, which provides clues to the composition of exoplanet atmospheres,”

says Odette Toloza from the University of Warwick, who developed a model for the disc of gas surrounding the white dwarf.

“The discovery also opens up a new window into the final fate of planetary systems,”

adds Gänsicke.

Stars like our Sun burn hydrogen in their cores for most of their lives. Once they run out of this fuel, they puff up into red giants, becoming hundreds of times larger and engulfing nearby planets. In the case of the Solar System, this will include Mercury, Venus, and even Earth, which will all be consumed by the red-giant Sun in about 5 billion years. Eventually, Sun-like stars lose their outer layers, leaving behind only a burnt-out core, a white dwarf. Such stellar remnants can still host planets, and many of these star systems are thought to exist in our galaxy. However, until now, scientists had never found evidence of a surviving giant planet around a white dwarf. The detection of an exoplanet in orbit around WDJ0914+1914, located about 1500 light years away in the constellation of Cancer, may be the first of many orbiting such stars.

According to the researchers, the exoplanet now found with the help of ESO’s X-shooter orbits the white dwarf at a distance of only 10 million kilometres, or 15 times the solar radius, which would have been deep inside the red giant. The unusual position of the planet implies that at some point after the host star became a white dwarf, the planet moved closer to it. The astronomers believe that this new orbit could be the result of gravitational interactions with other planets in the system, meaning that more than one planet may have survived its host star’s violent transition.

“Until recently, very few astronomers paused to ponder the fate of planets orbiting dying stars. This discovery of a planet orbiting closely around a burnt-out stellar core forcefully demonstrates that the Universe is time and again challenging our minds to step beyond our established ideas,”

concludes Gänsicke.

This chart shows the location of WDJ0914+1914 in the constellation of Cancer (The Crab). This map shows most of the stars visible to the unaided eye under good conditions, and WDJ0914+1914 itself is highlighted with a red circle on the image. This white dwarf is orbited by a Neptune-like exoplanet that is evaporating, the first ever giant planet found around a white dwarf.

Links

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Fire in the Sky:
Cosmic Collisions, Killer Asteroids, and
the Race to Defend Earth

Astronomy, Exoplanets

Video: “The Golden Age of Exoplanet Exploration”

At a public seminar at NASA JPL, Jessie Christiansen and Karl Stapelfeldt of Caltech and NASA talked about the exoplanets discoveries made thus far and those to be made by new observatories:

Since the discovery of the first exoplanet orbiting a sun-like star in 1995, several thousand more have been discovered. We’ve peered into the atmospheres of some, and we’ve found whole families of planets orbiting strange stars — many in configurations starkly different from our own. We’ve learned a lot from NASA’s Kepler mission, which launched 10 years ago and ceased operations in November 2018. A new NASA planet-hunting spacecraft called TESS, which began science operations as Kepler was winding down, will give us thousands of new discoveries in the coming years. And the Spitzer Space Telescope has provided us valuable insights into what these worlds might be like. This show will look at the state of exoplanet science and give us a view of what future discoveries may be around the corner.

This National Geo video gives a brief overview of exoplanets and how they are found and studied:

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Chasing New Horizons: Inside the Epic First Mission to Pluto

Astronomy, Exoplanets

ESO: Evidence found for super-earth orbiting Barnard’s Star

Here is the latest ESO (European Southern Observatory) report:

Super-Earth Orbiting Barnard’s Star
Red Dots campaign uncovers compelling evidence
of exoplanet around closest single star to Sun

The nearest single star to the Sun hosts an exoplanet at least 3.2 times as massive as Earth — a so-called super-Earth. Data from a worldwide array of telescopes, including ESO’s planet-hunting HARPS instrument, have revealed this frozen, dimly lit world. The newly discovered planet is the second-closest known exoplanet to the Earth and orbits the fastest moving star in the night sky. This image shows an artist’s impression of the planet’s surface. [Higher-res images]

The nearest single star to the Sun hosts an exoplanet at least 3.2 times as massive as Earth — a so-called super-Earth. One of the largest observing campaigns to date using data from a world-wide array of telescopes, including ESO’s planet-hunting HARPS instrument, have revealed this frozen, dimly lit world. The newly discovered planet is the second-closest known exoplanet to the Earth. Barnard’s star is the fastest moving star in the night sky.

A planet has been detected orbiting Barnard’s Star, a mere 6 light-years away. This breakthrough — announced in a paper published today in the journal Nature — is a result of the Red Dots and CARMENES projects, whose search for local rocky planets has already uncovered a new world orbiting our nearest neighbour, Proxima Centauri.

The planet, designated Barnard’s Star b, now steps in as the second-closest known exoplanet to Earth [1]. The gathered data indicate that the planet could be a super-Earth, having a mass at least 3.2 times that of the Earth, which orbits its host star in roughly 233 days. Barnard’s Star, the planet’s host star, is a red dwarf, a cool, low-mass star, which only dimly illuminates this newly-discovered world. Light from Barnard’s Star provides its planet with only 2% of the energy the Earth receives from the Sun.

Despite being relatively close to its parent star — at a distance only 0.4 times that between Earth and the Sun — the exoplanet lies close to the snow line, the region where volatile compounds such as water can condense into solid ice. This freezing, shadowy world could have a temperature of –170 ℃, making it inhospitable for life as we know it.

Named for astronomer E. E. Barnard, Barnard’s Star is the closest single star to the Sun. While the star itself is ancient — probably twice the age of our Sun — and relatively inactive, it also has the fastest apparent motion of any star in the night sky [2]. Super-Earths are the most common type of planet to form around low-mass stars such as Barnard’s Star, lending credibility to this newly discovered planetary candidate. Furthermore, current theories of planetary formation predict that the snow line is the ideal location for such planets to form.

Previous searches for a planet around Barnard’s Star have had disappointing results — this recent breakthrough was possible only by combining measurements from several high-precision instruments mounted on telescopes all over the world [3].

“After a very careful analysis, we are 99% confident that the planet is there,” stated the team’s lead scientist, Ignasi Ribas (Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain). “However, we’ll continue to observe this fast-moving star to exclude possible, but improbable, natural variations of the stellar brightness which could masquerade as a planet.”

Among the instruments used were ESO’s famous planet-hunting HARPS and UVES spectrographs.

“HARPS played a vital part in this project. We combined archival data from other teams with new, overlapping, measurements of Barnard’s star from different facilities,”

commented Guillem Anglada Escudé (Queen Mary University of London), co-lead scientist of the team behind this result [4].

“The combination of instruments was key to allowing us to cross-check our result.”

The astronomers used the Doppler effect to find the exoplanet candidate. While the planet orbits the star, its gravitational pull causes the star to wobble. When the star moves away from the Earth, its spectrum redshifts; that is, it moves towards longer wavelengths. Similarly, starlight is shifted towards shorter, bluer, wavelengths when the star moves towards Earth.

Astronomers take advantage of this effect to measure the changes in a star’s velocity due to an orbiting exoplanet — with astounding accuracy. HARPS can detect changes in the star’s velocity as small as 3.5 km/h — about walking pace. This approach to exoplanet hunting is known as the radial velocity method, and has never before been used to detect a similar super-Earth type exoplanet in such a large orbit around its star.

“We used observations from seven different instruments, spanning 20 years of measurements, making this one of the largest and most extensive datasets ever used for precise radial velocity studies.” explained Ribas. ”The combination of all data led to a total of 771 measurements — a huge amount of information!”

“We have all worked very hard on this breakthrough,” concluded Anglada-Escudé. “This discovery is the result of a large collaboration organised in the context of the Red Dots project, that included contributions from teams all over the world. Follow-up observations are already underway at different observatories worldwide.”

This wide-field image shows the surroundings of the red dwarf known as Barnard’s Star in the constellation of Ophiuchus (the Serpent-Bearer). This picture was created from material forming part of the Digitized Sky Survey 2. The centre of the image shows Barnard’s Star captured in three different exposures. The star is the fastest moving star in the night sky and its large apparent motion can be seen as its position changes between successive observations — shown in red, yellow and blue. [Higher-res images]
Notes
[1] The only stars closer to the Sun make up the triple star system Alpha Centauri. In 2016, astronomers using ESO telescopes and other facilities found clear evidence of a planet orbiting the closest star to Earth in this system, Proxima Centauri. That planet lies just over 4 light-years from Earth, and was discovered by a team led by Guillem Anglada Escudé.

[2] The total velocity of Barnard’s Star with respect to the Sun is about 500 000 km/h. Despite this blistering pace, it is not the fastest known star. What makes the star’s motion noteworthy is how fast it appears to move across the night sky as seen from the Earth, known as its apparent motion. Barnard’s Star travels a distance equivalent to the Moon’s diameter across the sky every 180 years — while this may not seem like much, it is by far the fastest apparent motion of any star.

[3] The facilities used in this research were: HARPS at the ESO 3.6-metre telescope; UVES at the ESO VLT; HARPS-N at the Telescopio Nazionale Galileo; HIRES at the Keck 10-metre telescope; PFS at the Carnegie’s Magellan 6.5-m telescope; APF at the 2.4-m telescope at Lick Observatory; and CARMENES at the Calar Alto Observatory. Additionally, observations were made with the 90-cm telescope at the Sierra Nevada Observatory, the 40-cm robotic telescope at the SPACEOBS observatory, and the 80-cm Joan Oró Telescope of the Montsec Astronomical Observatory (OAdM).

[4] The story behind this discovery will be explored in more detail in this week’s ESOBlog.

Links