The new exoplanet hunter

by Prasad Ganti

The Falcon 9 rocket blasted off into space like what has now become a routine launch. This time the payload was a space telescope on a mission, a more powerful set of eyes, peeping into the heavens for worlds beyond our own, to prove that we and our home planet are not all that unique in the Universe.

It is only in the last decade or so that we have been identifying planets orbiting other stars. Having overcome some of the technical challenges to detect something which is not easily visible, Which does not have light of its own, unlike the stars, whose reflection of the starlight is way too feeble. Which causes a very slight dimming of light when it comes in front of its parent star. Which causes its parent star to wobble very slightly as it goes around and around.

The current space telescope Kepler, was a pathfinder in terms of identifying about four thousand such exoplanets. While most of them were far and bigger than our own Earth. Being the first generation of such a finder, the telescope had its own limitations. It looked at only a small patch of the sky. And at stars thousands of light years away.

The new satellite called TESS (Transit Exoplanet Survey Satellite) will continue the legacy. It will be more focused in terms of detecting smaller planets (between the sizes of our own Earth and that of Neptune) and which are closer to us. Closeness is a relative term in astronomy. TESS will focus on a few tens or hundreds of light years, which is still far enough for a human visit. Smaller planets are likely to be rocky and at appropriate distance from the stars called the goldilocks zone, likely to host life. Also, relative proximity to our solar system can make the candidates amenable for more detailed study using other telescopes, both ground and space based.

While Kepler is on its last legs, having been a trailblazer, technology has advanced on our planet. TESS gains from such advances. Powerful cameras – four 16.8-megapixel cameras, each camera having seven lenses, which funnel light from the heavens toward four CCD (Charge Coupled Devices) image sensors which have been custom built by MIT’s (Massachusetts Institute of Technology) Lincoln labs. A single camera can cover a patch of sky 24 degrees wide by 24 degrees high. TESS’s main mission is to sweep almost the entire sky and focus on nearby stars. The search will be for about 200,000 relatively bright, pre-selected stars. The candidate red-dwarf stars are not big. They are not too bright, but because of shorter distances, appear brighter. Such stars live longer, burning their fuel at a slower rate. The longer life gives a greater chance for life to evolve on its planets.

Now a word about the orbit of this space telescope. It is an highly elliptical orbit. An ellipse is a stretched out circle. The stretching is pretty significant in this case. It will travel out as far as the moon is away from Earth, and then come back very close to the Earth every fourteen days. Most of the time spent away from the Earth, will protect it from the Earth’s Van Allen radiation belts. After all, space is a very hostile environment. Both to life as well as to spacecraft.

When TESS comes very close to the Earth, it will beam down data at a higher bandwidth. We understand the power of high bandwidth mobile networks like 4G or 5G when it comes to showing us videos on our phones. And TESS will collect huge amounts of data which needs to be analyzed for exoplanet detection. This highly elongated orbit is the first for any spacecraft. It will keep TESS very stable for longer time with minimal fuel consumption. Using a combination of Earth’s and moon’s gravity, it will need to burn very little fuel to keep moving.

The cameras will observe a vertical strip of the space stretching from the Earth’s pole to its equator in each orbit. Proceeding to the new neighboring strip in the next orbit, about twenty seven days later. It will take about one year to scan the heavens above the southern hemisphere and another year to finish the northern hemisphere. By the end of its two-year primary mission, it will have imaged roughly eighty five percent of the sky.

TESS will enable mankind to learn more about the other worlds. Certainly exciting times to be living in.

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This entry was posted in May 2018, Sidereal Times and tagged , . Bookmark the permalink.

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