The Kepler in TESS

By the end of September, the first science grade K2 observations from Campaign 0  should be  made available to the astronomical community and the public. Stayed tuned to this space for updates on the data release and how we’re making Planet Hunters ready to accommodate the K2 observations. While we eagerly await the public release of the first full science grade data from K2, I’ve been thinking about how K2 serves as a stepping stone to TESS, which is expected to launch in 3 years from now.

Over its 2 year mission, TESS is going to monitor ~200,000 of the  brightest stars across the sky for the signs of exoplanet transits by taking measurements of the stars’ brightness every 2 minutes. Most of these stars will be observed for only  27 days in total (though some patches of sky will be observed longer –  see the expected sky coverage plot below) , but the worlds discovered around these bright stars, unlike most of the Kepler planet candidates and confirmed planets,  will be able to be followed-up using ground-based techniques and technology as well as from the space-based James Webb Space Telescope (JWST). This will enable astronomers to probe the composition and structure of these planets’ atmospheres as well as their bulk composition.

Expected TESS sky coverage from Ricker et al. (2014)


One thing that I hadn’t appreciated from TESS was the engineering images  it will take in addition to the 2 minute light curves. TESS will target a small number of bright stars at a 2 minute cadence,  but every 30 minutes TESS will take the equivalent of a full frame engineering image across its  roughly 2000 square degree field-of-view. These means we basically get the equivalent of Kepler observations but with blurrier vision (Kepler had pixels that covered 4 arcseconds per pixel. TESS’s are much larger covering 21 arcseconds) and 20x more area. Below is a simulation generated of what a subsection of one of these engineering images might look like from a presentation by TESS principal investigator George Ricker at NASA’s Exoplanet Exploration Program Analysis Group (ExoPAG) meeting back in January.


Simulation of a portion of a TESS full frame engineering image – Image credit: TESS Team take from George Ricker’s January 2014 NASA’s Exoplanet Exploration Program Analysis Group (ExoPAG) presentation

We know from Kepler that it is possible to detect a plethora of exoplanet transits with 30 minute observations, so there is an exciting prospect of mining the engineering images. With the science that has already been done with Kepler both in the field of exoplanets and other astrophysics,  the TESS engineering images will no doubt be a treasure trove of data waiting to be tapped into.Before Kepler the only star that had been monitored to such precision and cadence was the Sun. Kepler has changed that, but TESS will take it to the next level.  With the Kepler-like quality of the engineering data, it means that if you don’t like the stars the TESS team decided to target, anyone can do an exoplanet search on other stars in the TESS field among other searches and studies like looking for supernovae or cataclysmic variables. There is a wealth of science to be mined out of the TESS full frame images, and I think there is a potential for citizen science (and likely Planet Hunters) to play a role in utilizing these observations to their fullest.

If you’re interested in learning more about the TESS spacecraft , camera design, and mission goals you can check out this paper by the TESS Team which is where I got the information for this post.


3 responses to “The Kepler in TESS”

  1. Art says :

    This short coverage time does not seem good for finding Earth-like planets as a large amount of transiting planets would be just missed or have insufficient number of transits. Also, what is photometric precision of TESS compared to Kepler?

    Was the field coverage, time and photometric precision chosen that way due to best science ÷ budget factor?

    • Meg says :

      Well you can find planets that are rocky and might potential have liquid water on their surfaces (in the habitable zone of the star) if that’s your definition of Earth-like around cooler stars than the Sun. The habitable zone of those stars would be closer in to the star so you could find those shorter period planets. Also there are regions that cover ~300 days and there with a TESS primary and hopefully extended mission you could detect rocky planets orbiting sun-like stars at 1 AU.

      • Art says :

        What about the photometric precision and signal to noise ratio? I heard that Kelper-421b was confirmed despite only two transit signals being detected. Yet it was confirmed despite not confirming it with other detection methods and being the only detected planet in the system. I also heard confirmation was possible due to high signal to noise ratio.

        How large are the 351-day coverage zones compared to Kepler field?

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