Astronomers estimate that up to 100 billion brown dwarfs make their home in our Milky Way Galaxy. Yet it remains unclear how they form—whether they are “failed” stars or possibly even super-planets. Now, scientists using the NSF’s NOIRLab and a team of data-sleuthing volunteers participating in Backyard Worlds: Planet 9, a citizen science project, have discovered roughly 100 cool worlds near the Sun — objects more massive than planets but lighter than stars that lack the mass needed to trigger nuclear fusion in their core, known as brown dwarfs. Several of these newly discovered worlds are among the very coolest known, with a few approaching the temperature of Earth — cool enough to harbor water clouds.
The study is evidence that the solar neighborhood “is still uncharted territory and citizen scientists are excellent astronomical cartographers,” said co-author Jackie Faherty of the American Museum of Natural History. “Mapping the coldest brown dwarfs down to the lowest masses gives us key insights into the low-mass star formation process while providing a target list for detailed studies of the atmospheres of Jupiter analogs.”
NASA’s WISE spacecraft and other telescopes have discovered hundreds of brown dwarfs, a few with protoplanetary disks around them, raising the possibility of detecting exoplanets orbiting them that might be able support alien life as we know it.
“These planets could be like the Earth, but they are relatively unstudied,” said Rory Barnes, a planetary scientist and astrobiologist at the University of Washington and the lead author of a 2014 study of brown and white dwarfs, which slowly cool and become less luminous over time with their habitable zones gradually shrinking inward and “face a difficult path to habitability.”
“These planets, if we find them today in a current habitable zone, previously had to have gone through a phase which sterilized them forever,” Barnes said. So, even if they are found in the habitable zone, they are dead.
The New Worlds
Remarkably, astronomers using NSF’s NOIRLab facilities and a team of data-sleuthing volunteers have unearthed new residents of the Solar neighborhood with the discovery of some 100 new worlds near the Sun –several appear to be among the coolest known, with a few approaching the temperature of Earth — cool enough to harbor water clouds. The new discoveries by Backyard Worlds: Planet 9, a citizen science project, bridge a previously empty gap in the range of low-temperature brown dwarfs, objects more massive than planets but lighter than stars, identifying a long-sought missing link within the brown dwarf population.
“These cool worlds offer the opportunity for new insights into the formation and atmospheres of planets beyond the Solar System,” said Aaron Meisner from the National Science Foundation’s NOIRLab and the lead author of the research paper. “This collection of cool brown dwarfs also allows us to accurately estimate the number of free-floating worlds roaming interstellar space near the Sun.”
This major advancement was made possible with archival data from the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory (KPNO) and the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), which were made available through the Community Science and Data Center (CSDC), all programs of NSF’s NOIRLab. Large survey data sets were then made available to the Backyard Worlds volunteers using NOIRLab’s Astro Data Lab science platform.
Global Network of 100,000 Citizen Scientists
To help find our Sun’s coldest and nearest neighbors, the astronomers of the Backyard Worlds project turned to a worldwide network of more than 100,000 citizen scientists. These volunteers diligently inspect trillions of pixels of telescope images to identify the subtle movements of brown dwarfs and planets. Despite the abilities of machine learning and supercomputers, there’s no substitute for the human eye when it comes to scouring telescope images for moving objects.
1,500 Cold Worlds Near the Sun
The Backyard Worlds volunteers have already discovered more than 1,500 cold worlds near to the Sun, and their new paper paper presents roughly 100 of the coldest in that sample. According to Meisner, this is a record for any citizen science program by a factor of about 20, and 20 citizen scientists are listed as co-authors of the study. A handful of these cool worlds — which are among the very coldest brown dwarfs known — approach the temperature of Earth. NASA’s Spitzer Space Telescope provided the brown dwarf temperature estimates.
Citizen scientist, Astro Data Lab user, and paper co-author Jim Walla added, “It’s awesome to know that our discoveries are now counted among the Sun’s neighbors and will be targets of further research.”
Unlocking New Worlds in Vast Data Sets
Alongside the dedicated efforts of the Backyard Worlds volunteers, NOIRLab’s Astro Data Lab was instrumental in this research. The technical burden of downloading billion-object astronomical catalogs is typically insurmountable for individual investigators — including most professional astronomers.
“AstroData Lab’s open and accessible web portal allowed Backyard Worlds citizen scientists to easily query massive catalogs for brown dwarf candidates,” explained NOIRLab astronomer Stephanie Juneau, who helped introduce the citizen scientists to Astro Data Lab. Astro Data Lab also enables convenient matching between data sets from NOIRLab telescopes and external facilities, such as NASA’s WISE satellite, that jointly contributed to these brown dwarf discoveries.
“Vast modern data sets can unlock landmark discoveries, and it’s exciting that these could be spotted first by a citizen scientist,” concludes Meisner. “These Backyard Worlds discoveries show that members of the public can play an important role in reshaping our scientific understanding of our solar neighborhood.”
This research was presented in the paper Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project to appear in The Astrophysical Journal.
The Daily Galaxy, Jake Burba, via American Museum of Natural History
Image credit top of page: artist’s concept shows a brown dwarf with bands of clouds, thought to resemble those seen at Neptune and the other outer planets. NASA/JPL-Caltech