NASA just found a planet 'hiding' in TESS spacecraft data, all thanks to Einstein

NASA's exoplanet-hunting spacecraft TESS (Transiting Exoplanet Survey Satellite) has a new method for detecting worlds beyond the solar system. The technique relies on a phenomenon introduced by Einstein in his 1915 theory of gravity, general relativity, called gravitational microlensing.

The exoplanet in question is called Gaia23bra b. The first hints of this exoplanet were found in 2023 by the now-retired Gaia space telescope via the slight brightening of a star caused by a microlensing event.

TESS usually spots planets by the tiny drop in the light output from their parent star as they cross, or transit, its face. This technique is most effective for very large gas giants that orbit close to their star, so it most likely wouldn't work for Gaia23bra b, which has 1.6 times Jupiter's mass but orbits its star at a similar distance to Jupiter's orbit around the sun. Additionally, the transit method employed by TESS usually has a search radius of around 150 light-years. Gaia23bra b, however, orbits an orange dwarf star about 80 percent the size of the sun that is located 40,000 light-years away. Thus, to confirm the existence of this world, TESS had to learn a new trick.

"When TESS launched, no one expected it to ever be capable of finding this kind of planet," team member Diana Dragomir of the University of New Mexico said in a statement. "The discovery implies that there are probably other so-called microlensing planets hiding in TESS's data that we hadn't previously thought to look for."

Microlensing and the hunt for exoplanets

To understand what microlensing is, first we have to consider what general relativity says about the effect of objects with mass on space itself. Mass causes the very fabric of space and time, united as 4-dimensional spacetime, to warp. Gravity arises from that curvature. The greater the mass, the more extreme the warping and thus the greater the force of gravity.

Gaia23bra b was first hinted at when it acted as a gravitational lens, passing between Earth and a background star, causing the ever-so-slight brightening of that star. The exciting thing about TESS successfully using microlensing is that this offers a complementary technique of exoplanet detection capable of detecting planets that the transit method might miss.

"With microlensing, we can find smaller planets with greater orbital distances, including worlds in the habitable zone of their star and even farther away," team member Mallory Harris of the University of New Mexico said. "Microlensing events happen once, and they're gone — they don't repeat. I like to joke that we'll probably find the first Earth analog with microlensing, and then wave at it as it goes by because we'll never see it again.