Across the Universe
“Hot Jupiter” is the common name given to planets that are as giant as Jupiter, and located very close distances from their sun — 20 times closer than the earth to our sun, and thus much hotter. While this type of planet does not exist in our solar system, Hot Jupiters can be found around 1 percent of stars. Questions like “where and when do they form?” or “how fast do they move from the outer to the inner parts of their system?” are still debated in the scientific world.
Using the ESPaDOnS spectrograph on the Canada-France-Hawaii Telescope (CFHT) atop Maunakea last Dec., an international team of astronomers reported preliminary evidence that a planet orbits a 2-million year star. Such age is extremely young for a star; the equivalent of a one-week old baby if the billion-year star life were to be scaled to human life.
The planet, yet to be confirmed, has a mass slightly larger than Jupiter and orbits in only six days around its sun, qualifying it as a “Hot Jupiter” exoplanet — a planet orbiting another star than the sun. The planet remains unseen but astronomers believe they have observed the small perturbations or wiggles in the star’s orbit caused by the planet’s small gravitational pull on its host star.
In the solar system, rocky planets like the earth are found near the sun whereas giant planets like Jupiter and Saturn orbit much further out.
“Hence the surprise in 1995 when Mayor & Queloz first discovered a giant planet sitting very close to its host star” says Dr. Moutou, French astronomer at CFHT.
Since then, astronomers have demonstrated that such planets must form in the outer regions of the disk surrounding baby stars, then migrate inwards and yet avoid falling into the star. This planetary movement could happen either very early in their lives, or much later.
The recently announced discovery supports an early migration. Looking at newly-born stars in the Taurus stellar nursery about 450 light-years away, the team of astronomers using CFHT showed that one of them, nicknamed V830 Tau, exhibits signatures that closely resemble those caused by a Hot Jupiter.
Although informative about planet formation, young stars are extremely challenging to observe. Astronomers have used ESPaDOnS to observe the spectra or rainbow of V830 Tau. They looked for wiggles in the spectra that are the signatures of Hot Jupiters, but the young age of stars makes those perturbations more difficult to see.
“Being enormously active, baby stars are covered with huge spots hundreds of times wider than those of our sun, which generate perturbations in their spectra much larger than those caused by orbiting planets,” outlines the French leader of the team, Dr. Donati.
The team uses tomographic techniques inspired from medical imaging to unveil how dark and bright features are distributed across the star surface.
“This modeling allows us to compensate for the perturbations that spots generate in the spectra of young stars, and thus to regain the power of diagnosing the presence of close-in giant planets,” Dr. Malo explains, a CFHT astronomer from Canada.
Although more observations are required, this promising first result clearly helps solving the question of how exoplanets form.
Canada-France-Hawaii Telescope headquarters are located in Kamuela with the telescope on the summit of Maunakea. CFHT has been operational since 1979 and is a joint, non-profit facility funded by the National Research Councils of Canada & France and the University of Hawaii.