With no solar system to call home!
It was not that long ago that astronomers announced that our galaxy is loaded with lonely, free-floating planets. In fact, these objects are so alone, they sit quietly in the darkness of space without any companion planets or host suns. What’s more, these segregated masses may actually outnumber all the stars in our Milky Way galaxy.
It was this startling discovery that prompted the question: Where the heck did all these objects come from?
Now, a new study using data from NASA’s Wide-field Infrared Survey Explorer (WISE), and the Two Micron All Sky Survey (2MASS), has provided some new clues. Scientists have identified a free-floating, planetary-mass object within a young star family, known as the TW Hydrae Association. The newfound object has been named WISEA J114724.10-204021.3, or WISEA 1147 for short, and it is estimated to be 5 to 10 times the mass of Jupiter.
Of all the free-floating objects lost in space, WISEA 1147’s origin was just one of a few that astronomers could pinpoint — it is likely a brown dwarf, and not a planet. Brown dwarfs are like stars, but they lack the mass to undergo nuclear fusion and therefore do not shine brightly.
Since WISEA was found to be a member of the TW Hydrae family, which is about 150 light-years from Earth, astronomers knew that it must also be very young — only 10 million years old. And because planets require at least 10 million years to form, and likely much longer than that to get themselves kicked out of a solar system, WISEA 1147 is most likely a brown dwarf.
There are billions of these free-floating worlds throughout our galaxy, and some may be brown dwarfs, while others might be planets that have been kicked out of their solar systems. However, tracing their origins and determining whether they are planets or brown dwarfs is an extremely difficult task, precisely because they are so isolated.
"We are at the beginning of what will become a hot field — trying to determine the nature of the free-floating population and how many are planets versus brown dwarfs," said co-author Davy Kirkpatrick of NASA's Infrared Processing and Analysis Center (IPAC), at the California Institute of Technology in Pasadena, in a NASA press statement.
Astronomers discovered WISEA 1147 by rummaging through images taken of the entire sky by WISE in 2010 and 2MASS a decade earlier. They were looking for nearby, young brown dwarfs and used the images to see if objects moved significantly relative to other stars over time. The closer an object, the more it will appear to move against a backdrop of more distant stars, and by analyzing sky surveys taken about 10 years apart, the closer objects jumped out.
WISE and 2MASS are perfectly suited for finding low-mass objects and brown dwarfs because they detect infrared light. Brown dwarfs are not bright enough to be seen with visible-light telescopes, but their heat signatures light up when viewed in the infrared. In fact, WISEA 1147 was a brilliant “red” in the 2MASS images, which means that it’s dusty and young.
"The features on this one screamed out, 'I'm a young brown dwarf,'" said Adam Schneider of the University of Toledo in Ohio, lead author of the study, which has been accepted for publication in The Astrophysical Journal.
Astronomers want to study these lonely worlds because not only do they resemble planets, but they are also easier to investigate. Planets that are found around host stars, called exoplanets, are hard to view next to their bright stars. By researching objects like WISEA 1147, which does not have a host star, astronomers can learn more about their composition and weather patterns.
"We can understand exoplanets better by studying young and glowing low-mass brown dwarfs," explained Schneider. "Right now, we are in the exoplanet regime."