At the same time, new ground-based telescopes that should aid in the hunt are coming online. Further afield, all eyes are on NASA’s thrilling Habitable Worlds Observatory (HWO), set to launch in the 2040s with a clear goal in mind: produce images of Earthlike planets around other stars and look for signs of life.
“We are actually at a very special time,” says Vikki Meadows, PhD, an astrobiologist at the University of Washington who also runs NASA’s Virtual Planetary Laboratory, which studies exoplanet habitability. “For millennia, we have wondered: Are we alone in the Universe? It’s only now [that] we have both the scientific knowledge and the technology to try and answer that question.”
We hunt for exoplanets in a number of ways. One is by watching for wobbles in a star’s position caused by the gravitational tug of an orbiting planet, known as the radial velocity method. Another is by watching for the dip in a star’s light as a planet passes in front, known as the transit method. This method is relatively simple and allows you to watch many stars at once for dips in light but relies on the system being oriented to us in just the right way for a transit to occur.
Our Milky Way galaxy is home to an estimated 400 billion stars, the majority of which likely host at least one planet and often more. PLATO will use 26 cameras to stare at more than 200,000 stars in our galaxy, many of which will be bright Sunlike stars, for at least two years. In doing so, it will be capable of detecting many small rocky worlds transiting these stars.
Were it looking at our Solar System, the telescope would see “Mercury, Venus, and Earth,” says Ana Heras, PhD, an astronomer at ESA in the Netherlands and project scientist for PLATO.
While the exact number of rocky planets the telescope will find isn’t known for certain, Heras says the team estimates they might find “tens of exoplanets” similar to Earth, orbiting stars like our Sun on similar orbits, among many other planets.
How plentiful Earthlike planets are in the galaxy remains an open question, but so far, rocky worlds in the habitable zones of smaller red dwarf stars seem to be “pretty common,” says Meadows. One of the most notable examples is the TRAPPIST-1 system about 40 light-years away, where seven rocky planets orbit a red dwarf star, three in its habitable zone. Because red dwarf stars are smaller and dimmer than our Sun and more prone to extreme flaring events, it is not yet known how hospitable they are to life.