Exoplanet discoveries have become more commonplace since the first was discovered in the mid-1990s. The most popular method is the transit method. That’s when telescopes see a small dip in brightness of a distant star caused by a nearby planet. What makes the most recent exoplanet discovery unique is the star (Teegarden’s Star) sits very close to the plane of Earth’s orbit around the Sun.
That means a telescope in that star system could see Earth pass in front of the Sun. The first Earth transit from Teegarden’s Star will occur in 2044 with regular transits continuing until 2496 according to researchers. If there is life around the two planets and they have similar technology as us, they would have already seen Mercury pass in front of the Sun. That’s a whole bunch of ifs, but it’s fun to think that other star systems could potentially be seeing us with the same method we use to discover other planets.
Credit: Zechmeister et al.
While I just talked about the transit method, the pair of planets found around Teegarden’s Star was spotted with an instrument called CARMENES. It’s a spectrograph that can detect planets via radial velocities. It’s detecting the motion of a star’s orbit moving back and forth in response to a planet’s gravitational pull on it.
The point planets and stars orbit is called the barycenter. It’s the shared center of gravity between two bodies. Here’s a quick video explaining the concept using Jupiter and the Sun.
And here’s a GIF exaggerating the star’s wiggling effect.
The CARMENES instrument is sensitive enough to see this motion in the Teegarden’s Star system. Two planets were spotted. The inner world, dubbed Teegarden b, orbits once every 4.91 days. That’s a year on Earth in less than a week. The big headline is it has a minimum mass of just 1.05 times Earth’s.
The outer planet, Teegarden c, orbits every 11.41 days and has a minimum mass of 1.11 Earth’s.
Ok, but how potentially habitable are these two planets? First off, Teegarden Star is a red dwarf star which automatically means a tough hill for life as we know it to climb. Red dwarf stars tend to emit intense flares that can make short work of a planet’s atmosphere and any potential life.
Plus, the two planets orbit their star at extremely close distances, 3.8 million kilometers and 6.6 million kilometers. Compare that to Mercury, which orbits the Sun at about 60 million kilometers. That means Teegarden b and c are almost certainly tidally locked. Meaning, one side of the planet always faces the star. One side always sits in sunlight the other in constant darkness.
An atmosphere and liquid ocean could help with heat transfer, but the best spot for any life to flourish would be close to the terminator (the twilight zone where the day and night sides meet).
Still, researchers put Teegarden b’s chances of having a temperate surface environment at 60%. That’s a surface temperature between 0 and 50 degrees Celsius. Teegarden c has only a 3% chance of having a temperate surface environment.
Teegarden b and c are numbers 51 and 52 in the potentially habitable exoplanet catalog. As better telescopes and instruments are developed, astronomers will take another look at these planets to see what more we can learn from them.