The Kepler mission, launched in 2009, is looking to greatly improve our understanding of planets. Since beginning operation, the planet hunting spacecraft has made tentative identifications of over 1,200 planets, having spotted them as they transited their parent stars. However, these planets need confirmation from a more robust method, specifically the spectroscopically detected wobbles, before they’re added to the official list of extrasolar planets.
Thus far, confirmations have been slow to come; only 16 of the planets have been detected using other methods. But recently, astronomers using the Hobby-Eberly Telescope (HET), operated by the University of Texas, Austin have confirmed another.
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The planet, Kepler-15b, is the first confirmed by this unique telescope. As opposed to most observatories, the mirror at the HET does not track the stars. Instead, the mirror remains stationary and the detecting instruments are moved along the focal plane to track the object in question. While this doesn’t allow for the object to track the entire night, it does let astronomers get continuous observation of the target for up to 2 hours. This unusual configuration was estimated to reduce the construction costs by as much as 80%.
From the Kepler observations, the tentative planet was expected to have an orbital period of just under 5 days and would transit the parent star for 3.5 hours, dimming the star’s light by about 1.2%. Using this information, the expectation was that the planet should have a radius of 1.4 times that of Jupiter, putting it in the class of “hot-Jupiters”.
The observations by the HET were taken from March until November of 2010. The team used the telescope’s spectrometer to search for the signs of variation between 2 and 100 days. When analyzed for periodicity, the team independently confirmed a strong signal with a period of 4.94 days.
Using the new spectroscopic data, the team estimates the new planet has a mass of 0.66 Jupiter masses, and reduces the estimated radius to 0.96 times that of Jupiter, giving a mean density of ~.9 grams per cubic centimeter. The parent star contains high amounts of heavy elements and is tied with Kepler-6 for the most metal rich parent star of the Kepler findings. If the planet, being formed from the same interstellar cloud, has similar metallicity, then it could be expected that the presence of these additional heavy elements could help to shrink the planet.
The team also reports that they have observed other purported Kepler planets and intends to include the findings in an upcoming publication. Additionally, the HET is scheduled for a major upgrade starting later this year. This will include upgrades to the tracking assembly, as well as the fiber optics used in the spectroscope. Currently, this instrument is only capable of performing confirmations for Jovian massed planets, but once upgrades are complete, the team expects to be able to use the system to search for lower mass candidates in the mass range of Neptune and those in the “Super-Earth” category.