The best hidden player in a cosmic game of hide-and-seek has just been given away by its own gravitational attraction. For the first time ever, scientists have identified an invisible alien planet by just noticing the gravitational attraction it exerts on another planet, which has been observed. The game was won by the NASA’s Kepler Space Telescope.
An Alien World
Kepler detected one alien planet as it made a transit across the star it orbits. However, it was noticed that the transit started five minutes early and ended five minutes later than expected. This could only mean that another planetary body tugs on this planet speeding up or delaying its orbital speed. The observed planet has been named Kepler 19b and the unseen planet, Kepler 19c. This is the first time this technique known as transit timing variation or TTV has been used to figure out the existence of an exoplanet. The planetary system is 650 light years away in the constellation Lyra.
Sarah Ballard of Harvard-Smithsonian Center for Astrophysics explains it in naughty-next-door-kid jargon:
It’s like having someone play a prank on you by ringing your doorbell and running away. You know someone was there, even if you don’t see them when you get outside
What about Kepler 19c?
Almost nothing is known about Kepler 19c, except for the fact that it exists. Generally, all planets fall in two categories rocky planets and gas giants. Kepler 19c can be a rocky planet with an orbital period of about 5-7 days (i.e. it is really close to the host star, but light) or it can be a gas giant with an orbital period of 100 or 200 days (i.e. it is far off, but very massive). Both types would be able to exert similar gravitational influence on Kepler 19b.
Kepler 19c hasn’t been seen transiting the parent star, suggesting that the planes of orbit of Kepler 19b and 19c are oblique to one another. Kepler will keep looking. Kepler has done an excellent job in detecting exoplanets, detecting as many as 1235 planets in its first four months of operation.
The excitement and toil of such a search is the same as that of a murder mystery investigation, but happily without a victim. Did you just say, Elementary…? It is not!