Earthlike Planet Found by NASA’s TESS

Earthlike planets are the target of NASA and MIT’s Transiting Exoplanet Survey Satellite (TESS). This week TESS found its first earth-sized planet orbiting in its suns’ habitable zone. Find out why NASA scientists are calling this discovery “exciting.”

I don’t remember when I first came to understand that the stars were distant suns that likely had earthlike planets orbiting them. It may have been from the Superman comic books. Perhaps it was from the TV shows Lost in Space or Star Trek.  

They were always travelling from star to star and finding intelligent life on earthlike planets. Star Trek even had a category for earthlike planets. They were called “Class M.”

Science fiction was our generation’s mythos. It took the place of the fantasy stories and fairy tales of earlier generations. George Lucas made that explicit when he began the first Star Wars movie with the phrase, “long ago, in a galaxy far, far away…” Humans communicate by telling stories.


Everyone assumed that there were earthlike planets out there somewhere. When we looked out at the night sky, we couldn’t help but wonder whether someone was looking back at us from one of those stars. Strictly speaking, though, we didn’t know that back then.

Astronomers only proved that other stars have planets beginning in the 1990s. There was a false alarm when astronomer Peter Van de Kamp thought that he had detected a planet around Barnard’s Star in the early 60s. Unfortunately, experts now agree that he was mistaken. The wobble he identified in the star was caused by his own gear.

In 1991, Professor Andrew Lyn announced in the journal Nature that he had discovered a planet orbiting a pulsar. That seemed counterintuitive since pulsars are the result of star explosions that should wipe out any planets they have.  


He was asked to present his findings at the American Astronomical Society. Then, just a few weeks before the conference, he realized that he had made a mistake. He hadn’t corrected his calculations to allow for the fact that Earth’s orbit isn’t a perfect circle.  

He rechecked his math and found out he was wrong. Still, he went ahead with his presentation, where he announced to a ballroom full of his peers that his findings were flawed, and his discovery wasn’t real.

He received a standing ovation. John Bahcall, an astrophysicist at the Institute for Advanced Study, told Michael D. Lemonick of Slate that it was “the most honourable thing I’ve ever seen.”


The first confirmed discovery of a planet came in 1995 when Professor Michel Mayor and his team found the world we now call Dimidium. Planets like Dimidium are called “hot Jupiters”. They are gas giants like Jupiter, but they are closer to their suns with shorter orbits.

Of course, what everyone really wanted to know was whether there were earthlike planets in space. Specifically, we want to find earthlike planets that aren’t too far away.  Donald Goldsmith chronicles this in his book, Exoplanets: Hidden Worlds and the Quest for Extraterrestrial Life

That’s why MIT and NASA came together to launch the Transiting Exoplanet Survey Satellite (TESS). It was launched on April 18, 2018, and it has found 1,561 Tess Objects of Interest (TOIs). This includes 37 confirmed planets with more to come.


Last week, TESS hit paydirt. It discovered a planet that was the size of the Earth and orbiting in its Sun’s habitable zone. It’s only about 100 light-years away in the southern constellation Dorado. This earthlike planet is called TOI 700 d. This isn’t the very first earthlike planet scientists have discovered, but it’s a first for TESS itself.

Planet TOI 700 d is the outermost known planet orbiting that star. Of the four stars in that solar system, it’s the only one in the habitable zone. It’s earthlike in size, measuring about 20% larger than Earth.  

A year on TOI 700 d only lasts 37 days. TOI 700 d gets about 86% of the energy that we get from the Sun. The planets in its solar system have orbits similar to the moon. They only rotate once per orbit so that one hemisphere is always lit up by the Sun. A year and a day are the same thing on these worlds.


Staff at NASA and MIT are excited. Paul Hertz is the astrophysics division director at NASA Headquarters in Washington. He explained, “TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars. Discovering TOI 700 d is a key science finding for TESS.”

This earthlike planet’s star, TOI 700, is bright and close to Earth. It also doesn’t have any stellar flares. This makes it a perfect candidate for further study using ground-based telescopes. Astronomers hope to confirm that its inner and outer planets are made of rock like Earth. They also hope to confirm whether these earthlike planets have atmospheres in future missions.

Scientists have enough data from TOI 700 d to construct computer models based on a range of scenarios. They’ve created 20 three dimensional climate models. From these models, they can predict what the spectrum of TOI 700 d might look like.  


Then, as Gabrielle Engelmann-Suissa, a visiting research assistant at the Goddard Space Flight Center explained, “Someday, when we have real spectra from TOI 700 d, we can backtrack, match them to the closest simulated spectrum, and then match that to a model. It’s exciting because no matter what we find out about the planet, it’s going to look completely different from what we have here on Earth.”

For many people, the main thing they want to know about astronomy and space exploration is whether there is life out there in the universe. We all have a deep longing to know whether or not we are alone in the universe. Locating earthlike planets is the first step toward answering that question.  

Even so, it’s only the beginning. We also need to pin down whether earthlike planets have atmospheres and water. Even then, we can’t be sure that this means there is life on them. It’s vital to keep identifying them, though, because then scientists can narrow down where they need to apply new techniques to respond to these unanswered questions.

We always have more to learn if we dare to know.

Learn more:

The First Habitable Zone Earth-sized Planet from TESS. I: Validation of the TOI-700 System
Astrobiology: 3 Questions We Need to Answer
Exoplanet Water Common Yet Rare
Exoplanet Giant Orbiting Tiny White Dwarf
Why Mars? Why Not Life on Venus?

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