Although we’ve found planets in binary star systems, it isn’t clear how they could have formed. But new observations of a binary system provides a clue.
Countless Worlds
One of the biggest advances of astronomy in the past decade has been the discovery of planets orbiting other stars, known as exoplanets. But just how many exoplanets have been discovered? According to the Extrasolar Planet Encyclopedia, a semi-official catalog based in Europe, there were as of the end of September last year 990 confirmed exoplanets and 2,321 candidate exoplanets. The discrepancy between these numbers has to do with the limitations of the observational data we currently have.
Mission Impossible
There’s news this week of an “impossible” triple star system recently discovered by astronomers. One that “defies known physics.” Needless to say, there’s no need to abandon physics quite yet.
Water in the Sky
The transit method of exoplanet observation looks at the light from a star to observe dips in brightness. When a planet passes in front of a star (transits), it blocks some of the starlight, making the star appear slightly dimmer. Normally when we are looking for exoplanets we simply look for an overall dip in brightness, from which we can determine things such as the size of the planet relative to the star.
But once an exoplanet is known, you can begin to make more subtle observations, such as observing the dip at different wavelengths. This was done by a team recently to study the atmosphere of an exoplanet known as Gliese 1214 b. Their results were recently published in the Astrophysical Journal.
Gravel Road
We have a pretty good idea of how planets form around stars. We know that dust is formed from the remnants of supernovae, that protoplanetary disks of dust form around young stars, and that dust grains can clump together to form pebbles. We also know how larger planetoids can drive the formation of planets, and how planets can migrate from their point of origin to their stable orbits. But there are still gaps in our understanding.
Going Rogue
A rogue planet is a planet-sized object that doesn’t orbit a star. Instead these objects move through the galaxy just as stars do. They’ve long been thought to exist, but their small size and low temperatures made them difficult to observe.
Cloudy with a Chance of Star
WISE J0855-0714 is a brown dwarf about 7 light years from us. Based upon its temperature, it is estimated to have a mass of about 10 Jupiters. The minimum mass to be considered a star is usually taken as 13 Jupiter masses, so this particular brown dwarf is either a very, very small star or (more likely) a very large Jupiter-type planet. That makes it either the 4th most distant star system or the closest known rogue planet. What we know for sure is that it is the coldest known brown dwarf, with a surface temperature of about 260 K (or 25 degrees below freezing for us Americans). It may also have a rather interesting atmosphere.
Snow Queen
Kepler-421b is a cold world orbiting a star about 1,000 light years away. At least according to a new paper announcing its discovery. This work hasn’t yet been peer reviewed, but it looks quite promising. What makes the discovery a big deal is that it is the longest period planet to be discovered by the transit method.
Needle in a Haystack
Just how difficult is it to discover a planet moving around another star? The Kepler space telescope finds planets by observing the brightness of stars over long periods. If a planet passes in front of its star, the light will dim slightly. But it doesn’t dim very much, so it takes some serious data analysis to discover.