Nav: Home

Devourer of planets? Princeton researchers dub star 'Kronos'

October 12, 2017

In mythology, the Titan Kronos devoured his children, including Poseidon (better known as the planet Neptune), Hades (Pluto) and three daughters.

So when a group of Princeton astronomers discovered twin stars, one of which showed signs of having ingested a dozen or more rocky planets, they named them after Kronos and his lesser-known brother Krios. Their official designations are HD 240430 and HD 240429, and they are both about 350 light years from Earth.

The keys to the discovery were first confirming that the widely separated pair are in fact a binary pair, and secondly observing Kronos' strikingly unusual chemical abundance pattern, explained Semyeong Oh, a graduate student in astrophysical sciences who is lead author on a new paper describing Kronos and Krios. Oh works with David Spergel, the Charles A. Young Professor of Astronomy on the Class of 1897 Foundation and director of the Flatiron Institute's Center for Computational Astrophysics.

Other co-moving star pairs have had different chemistries, Oh explained, but none as dramatic as Kronos and Krios.

Most stars that are as metal-rich as Kronos "have all the other elements enhanced at a similar level," she said, "whereas Kronos has volatile elements suppressed, which makes it really weird in the general context of stellar abundance patterns."

In other words, Kronos had an unusually high level of rock-forming minerals, including magnesium, aluminum, silicon, iron, chromium and yttrium, without an equally high level of volatile compounds -- those that are most often found in gas form, like oxygen, carbon, nitrogen and potassium.

Kronos is already outside the galactic norm, said Oh, and in addition, "because it has a stellar companion to compare it to, it makes the case a little stronger."

Kronos and Krios are far enough apart that some astronomers have questioned whether the two were in fact a binary pair. Both are about 4 billion years old, and like our own, slightly older sun, both are yellow G-type stars. They orbit each other infrequently, on the order of every 10,000 years or so. An earlier researcher, Jean-Louis Halbwachs of the Observatoire Astronomique of Strasbourg, had identified them as co-moving -- moving together -- in his 1986 survey, but Oh independently identified them as co-moving based on two-dimensional astrometric information from the European Space Agency's Gaia mission.

During a group research discussion at the Flatiron Institute, a colleague suggested pooling their data sets. John Brewer, a postdoctoral researcher from Yale University visiting at Columbia University, had been using data from the Keck Observatory on Mauna Kea, Hawaii, to calculate the spectrographic chemistries and radial velocities of stars.

"John suggested that maybe we should cross-match my co-moving catalogue with his chemical-abundance catalogue, because it's interesting to ask whether they have the same compositions," Oh said.

Binary stars should have matching radial velocities, but that information hadn't been available in the Gaia dataset, so seeing their matching velocities in Brewer's data supported the theory that Kronos and Krios, though two light years apart, were a binary set.

Then the researchers noticed the extreme chemical differences between them.

"I'm very easily excitable, so as soon as they had the same radial velocities and different chemistry, my mind already started racing," said Adrian Price-Whelan, a Lyman Spitzer, Jr. Postdoctoral Fellow in Astrophysical Sciences and a co-author on the paper.

Oh took more convincing, both scientists recalled. "Semyeong is careful and was skeptical," said Price-Whelan, so her first step was to double-check all the data. Once simple error had been ruled out, they began entertaining various theories. Maybe Kronos and Krios had accreted their planetary disks at different times during stellar formation. That one can't be tested, said Price-Whelan, but it seems unlikely.

Maybe they only started moving together more recently, after trading partners with another pair of binary stars, a process known as binary exchange. Oh ruled that out with "a simple calculation," she said. "She's very modest," Price-Whelan noted.

Oh's skepticism was finally overcome when she plotted the chemical abundance pattern as a function of condensation temperature -- the temperatures at which volatiles condense into solids. Condensation temperatures play a key role in planetary formation because rocky planets tend to form where it's warm -- closer to a star -- while gas giants form more easily in the colder regions far from their star.

She immediately observed that all of the minerals that solidify below 1200 Kelvin were the ones Kronos was low in, while all the minerals that solidify at warmer temperatures were abundant.

"Other processes that change the abundance of elements generically throughout the galaxy don't give you a trend like that," said Price-Whelan. "They would selectively enhance certain elements, and it would appear random if you plotted it versus condensation temperatures. The fact that there's a trend there hinted towards something related to planet formation rather than galactic chemical evolution."

That was her "Aha!" moment, Oh said. "All of the elements that would make up a rocky planet are exactly the elements that are enhanced on Kronos, and the volatile elements are not enhanced, so that provides a strong argument for a planet engulfment scenario, instead of something else."

Oh and her colleagues calculated that gaining this many rock-forming minerals without many volatiles would require engulfing roughly 15 Earth-mass planets.

Eating a gas giant wouldn't give the same result, Price-Whelan explained. Jupiter, for example, has an inner rocky core that could easily have 15 Earth masses of rocky material, but "if you were to take Jupiter and throw it into a star, Jupiter also has this huge gaseous envelope, so you'd also enhance carbon, nitrogen -- the volatiles that Semyeong mentioned," he said. "To flip it around, you have to throw in a bunch of smaller planets."

While no known star has 15 Earth-sized planets in orbit around it, the Kepler space telescope has detected many multi-planet systems, said Jessie Christiansen, an astronomer at the NASA Exoplanet Science Institute at the California Institute of Technology, who was not involved in the research. "I see no problem with there being more than 15 Earth masses of accretable material around a solar-type star." She pointed to Kepler-11, which has more than 22 Earth masses of material in six planets with close orbits, or HD 219134, which has at least 15 Earth masses of material in its inner four planets.

"At the moment, we are still at the stage of piecing together different observations to determine how and when exoplanets form," said Christiansen. "It's difficult to directly observe planet formation around young stars -- they are typically shrouded in dust, and the stars themselves are very active, which makes it hard to disentangle any signals from the planets. So we have to infer what we can from the limited information we have. If borne out, this new window onto the masses and compositions of the material in the early stages of planetary systems may provide crucial constraints for planet formation theories."

The research also has implication for stellar formation models, noted Price-Whelan.

"One of the common assumptions -- well-motivated, but it is an assumption -- that's pervasive through galactic astronomy right now is that stars are born with [chemical] abundances, and they then keep those abundances," he said. "This is an indication that, at least in some cases, that is catastrophically false."
-end-
The Flatiron Institute is the intramural research division of the Simons Foundation. This work has made use of data from the European Space Agency mission Gaia, processed by the Gaia Data Processing and Analysis Consortium, which is funded by the institutions participating in the Gaia Multilateral Agreement. This work also used data products from the Two Micron All Sky Survey, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, (Caltech), funded by the National Aeronautics and Space Administration (NASA) and the National Science Foundation. This research made use of data products from the Wide-field Infrared Survey Explorer, a joint project of the University of California-Los Angeles, and the Jet Propulsion Laboratory/Caltech, funded by NASA.

Princeton University

Related Planets Articles:

Ultracool dwarf and the 7 planets
Astronomers have found a system of seven Earth-sized planets just 40 light-years away.
ALMA measures size of seeds of planets
Researchers using the Atacama Large Millimeter/submillimeter Array (ALMA), have for the first time, achieved a precise size measurement of small dust particles around a young star through radio-wave polarization.
Origin of minor planets' rings revealed
A team of researchers has clarified the origin of the rings recently discovered around two minor planets known as centaurs, and their results suggest the existence of rings around other centaurs.
Are planets setting the sun's pace?
The sun's activity is determined by the sun's magnetic field.
A better way to learn if alien planets have the right stuff
A new method for analyzing the chemical composition of stars may help scientists winnow the search for Earth 2.0.
A new Goldilocks for habitable planets
The search for habitable, alien worlds needs to make room for a second 'Goldilocks,' according to a Yale University researcher.
Probing giant planets' dark hydrogen
Hydrogen is the most-abundant element in the universe, but there is still so much we have to learn about it.
Universe's first life might have been born on carbon planets
Our Earth consists of silicate rocks and an iron core with a thin veneer of water and life.
Number of habitable planets could be limited by stifling atmospheres
New research has revealed that fewer than predicted planets may be capable of harbouring life because their atmospheres keep them too hot.
Footprints of baby planets in a gas disk
A new analysis of the ALMA data for a young star HL Tauri provides yet more firm evidence of baby planets around the star.

Related Planets Reading:

The Planets
by Robert Dinwiddie (Author), Heather Couper (Author), John Farndon (Author), Nigel Henbest (Author), David Hughes (Author), Giles Sparrow (Author), Carole Stott (Author), Colin Stuart (Author)

Featuring all-new 3D models built using data gathered by NASA and the European Space Agency, The Planets is an awe-inspiring journey through the Solar System, from Earth to Mars and beyond.

Viewed layer by layer, planets and other objects in the Solar System are taken out of the night sky and presented on a white background, revealing every detail of their surface and internal anatomy in astonishing detail.

Looking at planets, the Sun, hundreds of moons and thousands of asteroids and comets, The Planets includes timelines that chronicle all major Space missions, right... View Details


The Planets: Photographs from the Archives of NASA
by Nirmala Nataraj (Author), NASA (Photographer), Bill Nye (Photographer)

This magnificent volume offers a rich visual tour of the planets in our solar system. More than 200 breathtaking photographs from the archives of NASA are paired with extended captions detailing the science behind some of our cosmic neighborhood's most extraordinary phenomena. Images of newly discovered areas of Jupiter, fiery volcanoes on Venus, and many more reveal the astronomical marvels of space in engrossing detail. Anyone with an interest in science, astronomy, and the mysteries of the universe will delight in this awe-inspiring guide to the wonders of the solar system. View Details


Planets
by Ellen Hasbrouck (Author), Scott McDougall (Illustrator)

Take a trip through the solar system and discover what¹s really up in the sky! Packed with fascinating facts about planets, comets, asteroids and more, Planets is a galaxy of fun for young astronomers...and everybody who gazes at the night sky!
Create your own universe and solar system with reusable stickers of the planets, asteroids, galaxies, and comets! View Details


National Geographic Readers: Planets
by Elizabeth Carney (Author)

This brilliantly illustrated book taps into children's natural curiosity about the vast world of space. This level 2 reader, written in simple language that is easy for young readers to understand, introduces children to our solar system, including all of the planets and dwarf planets, and lots of fascinating fun facts. This reader helps cultivate the explorers of tomorrow!

This high-interest, educationally vetted series of beginning readers features the magnificent images of National Geographic, accompanied by texts written by experienced, skilled children's book authors. The inside... View Details


The Dinosaur That Pooped a Planet!
by Tom Fletcher (Author), Dougie Poynter (Author), Garry Parsons (Illustrator)

From Tom Fletcher and Dougie Poynter of McFly comes a supersonic space adventure filled with planets, poop, and pandemonium!

One boy, one space rocket, one very hungry dinosaur: the ingredients for an explosive space adventure of epic poop-portions! But when Danny realizes he’s forgotten Dino’s lunch box, the very hungry dinosaur eats everything in sight, including their only way home: the rocket! How will Dino get them back home?

Meet Danny and his pet Dinosaur, Dino. No matter what this ravenous reptile ingests, he never keeps it down for long. View Details


13 Planets: The Latest View of the Solar System (National Geographic Kids)
by David A. Aguilar (Author)

First, Pluto left. Then it came back, along with Ceres and Eris...and now Haumea and MakeMake, too! The recent actions of the International Astronomical Union have put every solar system book out of date. In response, National Geographic joins forces with David Aguilar of the Harvard Smithsonian Astronomical Observatory to revise our 2008 book—and to update young readers on the high-interest topic of space. Using simple text and spectacular photorealistic computer art by the author, this book profiles all 13 planets in their newly created categories—plus the sun, the Oort Cloud, comets,... View Details


Planets (LEGO Nonfiction): A LEGO Adventure in the Real World
by Scholastic (Author)

Blast off with the LEGO(R) minifigures through our solar system and beyond! See incredible stars and planets and find out the latest space facts--from water on Mars to Planet X. The LEGO minifigures put the fun into facts. You'll find great LEGO building ideas, too!

LEGO(R) minifigures show you the world in a unique nonfiction program. This book is part of a program of LEGO nonfiction books, with something for all the family, at every age and stage. LEGO nonfiction books have amazing facts, beautiful real-world photos, and minifigures everywhere, leading the fun and... View Details


GOOD NIGHT, PLANET: TOON Level 2 (TOON Books, Level 2)
by Liniers (Author)

New York Times Notable Children’s Books of 2017
When you go off to sleep, your toys go out to play! After a long day of jumping in leaves and reading her favorite books, this little girl is wornout, but her favorite stuffed animal, Planet, is just getting started. Planet befriends a dog, gobbles a cookie, and takes a leap into the unknown. This tender, gorgeous tale by the internationally renowned cartoonist Liniers will reveal to early readers the wonders that exist at night, in secret, after they close their eyes.

Liniers's US debut, The... View Details


Lonely Planet Thailand (Travel Guide)
by Lonely Planet (Author), Mark Beales (Author), Tim Bewer (Author), Joe Bindloss (Author), Austin Bush (Author), David Eimer (Author), Bruce Evans (Author), Damian Harper (Author), Isabella Noble (Author)

#1 best-selling guide to Thailand*

Lonely Planet Thailand is your passport to the most relevant, up-to-date advice on what to see and skip, and what hidden discoveries await you. Wander through wild orchids in Mae Hong Son, charter a longtail boat on the Andaman Coast or look for tigers and monkeys in national parks; all with your trusted travel companion. Get to the heart of Thailand and begin your journey now!

Inside Lonely Planet Thailand Travel Guide:

Colour maps and images throughout Highlights and... View Details


National Geographic Little Kids First Big Book of Space (National Geographic Little Kids First Big Books)
by Catherine D. Hughes (Author), David A. Aguilar (Illustrator)

This beautiful book is the latest addition to the National Geographic Little Kids First Big Book series. These colorful pages will introduce young children to the wonders of space, with colorful illustrations by David Aguilar and simple text that is perfect for beginning readers or for reading aloud. The book will explain basic concepts of space, beginning with what is most familiar to kids and expanding out into the universe.

Chapters include:
 • Chapter 1 focuses on the Earth, moon, and sun.
 • Chapter 2 introduces kids to the other planets in our solar system.... View Details

Best Science Podcasts 2017

We have hand picked the best science podcasts for 2017. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Going Undercover
Are deception and secrecy categorically wrong? Or can they be a necessary means to an end? This hour, TED speakers share stories of going undercover to explore unknown territory, and find the truth. Guests include poet and activist Theo E.J. Wilson, journalist Jamie Bartlett, counter-terrorism expert Mubin Shaikh, and educator Shabana Basij-Rasikh.
Now Playing: Science for the People

#452 Face Recognition and Identity
This week we deep dive into the science of how we recognize faces and why some of us are better -- or worse -- at this than others. We talk with Brad Duchaine, Professor of Psychology at Dartmouth College, about both super recognizers and face blindness. And we speak with Matteo Martini, Psychology Lecturer at the University of East London, about a study looking at twins who have difficulty telling which one of them a photo was of. Charity Links: Union of Concerned Scientists Evidence For Democracy Sense About Science American Association for the Advancement of Science Association for Women...