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.
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,”
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,”
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:
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.
The planet, designated Barnard’s Star b, now steps in as the second-closest known exoplanet to Earth . 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 . 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 .
“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 .
“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.”
Notes  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.
 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.
Musk talks about humanity being a multi-planet species, in part as an insurance policy against earthly disasters, whether natural or manmade; he is particularly concerned about the potential danger to humanity posed by artificial intelligence. But he seems to consider two — Earth and Mars — to be a sufficient number for “multi.” Musk could in fact be accused of an extension of what Carl Sagan called “planetary chauvinism” — the belief that life can thrive only on planets. But many analysts, I included, don’t understand the motivation, once having finally escaped the deep gravity well that has confined us to the planet on which we evolved, to dive down into another, albeit a shallower one.
By contrast, Bezos, as noted, aims for a massive human expansion, and not only to many other planets but to inhabitance of space itself. Wealthier than Musk — on some days he is the world’s richest person — Bezos is also more willing to spend his own money. Last November he sold a billion dollars’ worth of Amazon stock and claims to intend to do the same every year to provide the rocket company with its annual stipend, and he recently built a large facility at NASA’s Kennedy Space Center in Florida to begin the manufacture of his large orbital rockets. Musk, on the other hand, always prefers, if he can find a way, to fund his dreams using OPM — Other Peoples’ Money. In the case of Tesla and its subsidiary SolarCity, which sells solar panels for home and commercial use, he’s done it with loans from Washington (which he has since paid off), various government subsidies for the production of electric cars, and tax credits offered to people buying electric cars or installing solar panels. In the case of SpaceX, extra funding has come, albeit in this case in exchange for providing a direct service, from NASA and U.S. Air Force contracts.
Over a decade and a half since both men launched their space companies, they have made significant progress in reducing the cost of getting to suborbital and orbital space. If their plans for large reusable launch systems come to fruition in the next few years, with SpaceX’s BFR and possibly Blue Origin’s New Armstrong offering larger payload capacities than NASA’s non-reusable Space Launch System, they may well render it obsolete before the full Block 2 version flies. (The planned first flight of the initial Block 1 configuration of SLS has slipped to the end of 2019.) Before its second flight — probably no sooner than a year after its first — it may well be canceled for good, not to be resurrected, perhaps finally putting a stake through the heart of Apolloism.
In July 2018, a disturbing video began circulating on social media. It shows two women and two young children being led at gunpoint away from a village by a group of soldiers. The victims are blindfolded before they are shot point blank 22 times. The social media posts claimed them to be from Cameroon but the government of Cameroon initially dismissed the video as “fake news”.
The video showed a terrain that could be from anywhere in the world, and the people could be anywhere from Africa. But BBC Africa Eye did a thorough investigation through forensic analysis of the footage. Among other things, they poured through satellite imagery of many years trying to match them with the landmarks in the video to prove exactly where and when this incident took place and who were responsible. The Cameroon government was forced to issue a statement clarifying their earlier stand and announced that a number of soldiers have been arrested and are under investigation now.
Satellite imagery has become an indispensable tool in journalism. Be it fact-finding or gauging the impact of a particular situation, reporting on climate events or conflict zones, because of the unbiased insights they provide, they are being extensively used by professional journalists today.