The NASA Kepler mission has found scores of Jupiter-sized candidate planets in other solar systems — but mostly, they have been so-called hot Jupiters, those that tightly hug their host stars in short period orbits. A true Jupiter analogue, however, one with a period of 12 years, just as in our solar system, has been lacking. And they hold plenty of interest for theorists, who think that our Jupiter was instrumental in creating the conditions for the Earth to form.
But could the Kepler data already hold Jupiter analogues, hiding in plain sight? “They’re going largely unnoticed by the Kepler team,” says Jennifer Burt, a graduate student at the University of California at Santa Cruz, who presented a poster on the subject at the Kepler Science Conference, which began on 5 December at Ames Research Center in Moffett Field, California.
Burt will try to identify Jupiters by being fundamentally less picky than the Kepler mission team, which requires three transits before a planet can even qualify as a candidate. (Kepler identifies planets by looking for small dips in starlight when the planet transits, or crosses the face of, its host.) To get a true Jupiter, the Kepler team, playing by its rules, would have to wait for three transits over the course of, at minimum, 24 years. The mission will long be over by then.
But Burt thinks that a Jupiter analogue could be identified based on a single transit, because its effects are so distinctive. A Jupiter transit would not only cause a pronounced reductions in starlight of about 1%, but would also last for a long time, about 30 hours.
In Kepler’s first three quarters of data, which were released in February, Burr expects that 18 Jupiter transits are hiding, based on Monte Carlo simulations. She has already culled 7,000 potential transits from 150,000 Kepler light curves, and is getting ready to embark on her next round of filtering.
When and if she finds a proper candidate, Burt will then have to convince her colleagues that it’s real. For that, she will need follow-up measurements from the ground-based telescopes, which look for tiny changes in the host star’s velocity caused by the planet at opposite ends of its orbit. Doing the follow-up the normal way would again require a long time — six years or more. But with a new instrument nearly ready for commissioning on the university’s 2.4-metre Automated Planet Finder Telescope, Burt thinks she could begin to see the shifts in velocity caused by a Jupiter after just three years, or a quarter of its orbit.
Image credit: NASA