Scienceline’s Guide to the Exoplanets: The Ice Dot
Rahul Rao • July 20, 2020
Your favorite planets, and you didn't even know they existed. [Credit: Curtis Segarra | CC BY-NC-ND 2.0]
The Ice Dot
Discovered by: Spitzer space telescope and Korea Astronomy and Space Science Institute
Mass: ~1.4 Earth masses
Surface climate: Frozen
Habitability for humans: Maybe, if you can find humans who can live in liquid nitrogen
Yes, OGLE-2016-BLG-1195Lb has a quite convoluted name. OGLE is abbreviated from something called the Optical Gravitational Lensing Experiment, a project run by the University of Warsaw in Poland that since the 1990s has gazed into the sky, seeking exoplanets. In fact, since the early 2000s, OGLE has discovered over a dozen exoplanets.
OGLE-2016-BLG-1195Lb, although it orbits a distant star around 13,000 light-years from Earth, wasn’t actually one of those exoplanets; instead, it was discovered by a team of astronomers using the Spitzer space telescope following up on an OGLE observation, in conjunction with astronomers from the OGLE-like Korea Microlensing Telescope Network.
OGLE-2016-BLG-1195Lb, when viewed from a far distance, isn’t entirely unlike Earth. It’s only very slightly more massive than the Earth, and roughly the same size. If it orbited something like Earth’s Sun, it might actually orbit in a rather similar place to the Earth, and might even bear liquid water upon its surface. Basically, in that situation, it could be habitable for Earth life.
The difference, then, lies in OGLE-2016-BLG-1195Lb’s star. As it turns out, the exoplanet does not orbit anything similar to Earth’s sun.
It instead orbits a star that’s much smaller: less than one-tenth the size of the Sun. It’s so lightweight and so small in size that astronomers aren’t even sure if it’s a star at all.
Some believe that the so-called star is actually a brown dwarf, living in the blurry transition zone between a very large gas planet and a small star. Others believe that it is, in fact, a star: an ultracool dwarf, a tiny, faint, slow-burning star that is surprisingly common.
In any event, the result is an Earth-sized planet that orbits in an Earth-sized orbit around a very cold sun. Scientists believe that OGLE-2016-BLG-1195Lb is one of the absolute coldest known exoplanets, with a temperature around 31 Kelvin, or less than negative 400 degrees Fahrenheit. On the surface of OGLE-2016-BLG-1195Lb, both the oxygen and the nitrogen that comprise so much of Earth’s atmosphere would freeze solid.
For comparison, Pluto — an utterly frigid ball — has a surface temperature averaging around 44 Kelvin. In contrast, OGLE-2016-BLG-1195Lb might not sound that impressive, but consider Pluto and how difficult it was to discover (in the 1930s and essentially completely by accident). Think about how difficult it was to even discover Neptune, a much larger planet, yet one that’s so distant from both Earth and its sun.
Now think about the fact that astronomers discovered this: a planet much smaller than Neptune, orbiting at a somewhat great distance from a star, an order of magnitude smaller than Earth’s sun, over ten thousand light-years away.