The Spacecraft Tarot: TESS

Tippy Ki Yay
5 min readJun 19, 2021
The original watercolor illustration is by me, Tippy Ki Yay. The background image is Hubble imagery and the credit belongs to NASA, ESA, and J. Olmsted (STScI).

Judgment provides us closure.

Sometimes judgment is needed to close or open a door on something — whether it is a relationship, a career, or a phase in our lives. Judgment can be a tool used for self-reflection. By taking a mental inventory of our circumstances, we can come closer to leaving the past behind and moving forward in the right direction. Judgment allows us to label, categorize, and reach finality.

NASA’s Transiting Exoplanet Survey Satellite (TESS) is the ultimate tool of judgment. TESS searches for planets outside of our solar system, also known as exoplanets. TESS’ tools of perception, especially when paired up with data from ground-based telescopes, can judge whether or not a blip of data is simply that or a newly-discovered world.

There are around 400 billion stars in our galaxy alone. Many if not all of those stars are orbited by planets, and these planets vary drastically in size, atmospheric conditions, and orbital durations. These planets can possess a diversity of colored skies. Their climates can be burning hot or deathly cold.

There have always been strong suspicions that planets exist outside of our own solar system. But it wasn’t until October 6, 1995 when this was confirmed by the discovery of 51 Pegasi b by astronomers Michael Mayor and Didier Queloz across two separate observatories. Using a method called radial velocity, or the “wobble” method, the astronomers used ground telescopes to observe a star being slightly jostled by the gravitational tug of another planet.

The discovery of 51 Pegasi b suggested that more exoplanets were out there. Even more exciting than the possibility of more exoplanets was the possibility of exoplanets existing in the habitable zone, also known as the “Goldilocks zone.” The habitable zone is the region around a star where a planet needs to exist in order to maintain the correct temperature to contain liquid water. Too hot, the water will turn to steam. Too cold, the water will turn to ice. But just warm enough, liquid water on another planet increases the possibility of life.

NASA’s Kepler spacecraft rises on United Launch Alliance’s Delta II rocket from Launch Pad 17-B at Cape Canaveral Air Force Station in Florida on March 6, 2009. Image Credit: NASA, Regina Mitchell-Ryall and Tom Farrar

In order to augment ground observatories’ ability to detect exoplanets — especially exoplanets in the habitable zone—NASA developed the Kepler spacecraft. The space-based telescope launched from Cape Canaveral Air Force Station in Florida on March 6, 2009.

During its four-year prime mission, Kepler used the “transit method” to detect planets orbiting around other stars. The spacecraft focused its gaze on other stars for long periods of time, measuring any changes in brightness that occur during that time period. Dips in brightness can indicate that a planet is passing in front of the sun and blocking some of the light getting through — also known as a “transit.”

Kepler discovered over 2,000 exoplanets using the transit method. In fact, scientists are still discovering planets embedded in past Kepler data.

Some of Kepler’s most important discoveries point to a universe where not only planets are vastly diverse from one another, but solar systems are as well. Systems vary in number of planets, and even number of stars.

Unfortunately, technical problems forced Kepler to end its first mission in 2013. Even with the spacecraft’s diminished pointing ability, Kepler still managed to embark on a second mission called K2. After discovering several hundred more exoplanets, Kepler was officially decommissioned in 2018.

Picking up where Kepler left off is TESS. TESS launched on April 18, 2018 from Cape Canaveral Air Force Station and settled into a fourteen-day orbit around the Earth. Like Kepler, TESS uses the transit method to identify possible candidates for exoplanets.

Although Kepler is credited for finding the most exoplanets of any mission so far, TESS is unique in that it can observe the sky at much larger intervals at a time. TESS uses four wide-field cameras that allow it to gaze at 24-by-96-degree strips of the sky — allowing the spacecraft to see 400 times the area Kepler observed.

TESS captured the 208 images used to stitch together this mosaic of the northern sky during the spacecraft’s second year of science operations, completed in July 2020. Image Credit: NASA/MIT/TESS and Ethan Kruse (USRA)

Because TESS focuses its gaze on stars that are brighter and closer to us than the stars that Kepler observed, TESS’ discoveries are more likely to able to be paired with observations from ground-based telescopes. To qualify as a possible exoplanet, an object must pass between TESS and a star at least three times. The supplemental data from ground-based telescopes help us confirm that TESS’ discoveries are in fact planets, and not interference from another light source like another star. If the candidate is confirmed to be a planet, spectrographs can also measure the planet’s mass, radius, and the duration of its orbit — providing us a clearer picture of our universe, one exoplanet at a time.

Since TESS launched, the spacecraft has discovered over 100 exoplanets and thousands of exoplanet candidates. Having completed its primary mission in July 2020 to image 75% of the sky, TESS is currently in its extended mission to continue observing transits and discovering exoplanets, using a faster mode of capturing data than before.

Just as Judgment can provide us closure in times of uncertainty, TESS is examining every crevice of the sky in search of exoplanets. The planet hunter measures light in order to pass judgment on exoplanet candidates — is it a planet? Or is it just a blip in the radar? The answers are helping us unlock answers to ancient questions: Are we unique? Are we alone?

Allow judgment to enter your life, answer your questions, and end the wondering.

A plot combining TESS northern and southern mosaics. Image Credit: NASA/MIT/TESS and Ethan Kruse (USRA)

Read the complete Spacecraft Tarot series.