The search for Earth-like planets has led to the discovery of planets in different galaxies, but which of them are most suited to creating conditions where life could flourish?
What Are Exoplanets and How Many Exist
Exoplanets (also called extrasolar planets) are any planets that aren’t in our Solar System. We’ve known about the existence of these objects for around a century, although it’s only in the last few decades that we’ve been also to confirm their presence.
At the time of writing, more than 5,800 exoplanets have been confirmed. These planets are found in over 4,300 planetary systems dotted across the universe and are found in a variety of ways like transit photometry and Doppler spectroscopy. There are many more planets still to be discovered.
Estimates vary, with some suggesting that there could be as many as 40 billion planets in the Milky Way that are roughly the size of Earth and could potentially be considered as being habitable. Could one of these planets already support life or could they offer the right conditional for humans to live elsewhere in the universe?
The Variety of Planets
The exoplanets we know about range in size from Draugr – only twice as big as the Moon – to HR 2562 b, which is 30 times the size of Jupiter. They also vary widely in terms of the time taken to orbit their respective stars. The closest takes under an hour, while others can take several thousand years to complete a single orbit.
While most of the exoplanets we know about are located in the Milky Way, evidence is growing that we will eventually find more in other galaxies, too. We also need to take into account the rogue planets that aren’t tied to a planetary system since they travel freely in space.
Planets Discovered So Far
51 Pegasi b was first observed in 1995, causing excitement in the scientific community as being the first exoplanet to be confirmed as orbiting a star similar to the Sun. 50 light years away from Earth, it’s half the size of Jupiter and rushes around its sun in a tight orbit. In 2017, some evidence of water was found in its atmosphere.
For the moment, Kelper-452b is often described as being the most Earth-like planet to have been discovered. Located 1,800 light-years away from us, it’s found in the Cygnus constellation and was announced to the world in 2015.
The similarities with Earth are striking. Kepler-452b orbits a star similar to our Sun and at almost the same distance as Earth’s orbit. It’s 1.6 times the size of our home planet and is likely to be slightly hotter than Earth. This is one of 12 exoplanets identified by NASA’s Kepler space telescope that are found in the habitable zone of a star and that are less than two times as big as Earth.
Other potentially habitable exoplanets include GJ 1002b and GJ 1002c. Both orbit a red dwarf star and fit the criteria thanks to being almost the same size as our planet. TOI-733 b was discovered in 2023 and is described as being in the Super Earth category since it’s 5.72 times the size of our planet.
TRAPPIST-1e in the Aquarius constellation is roughly 40.7 light-years away and is 0.692 the size of Earth. The fourth planet in its star’s system, it’s widely described as being one of the exoplanets most likely to be capable of supporting life.
What Comes Next
It seems certain that we continue to discover more exoplanets, but we can expect the majority of them to be so unlike Earth that the possibility of them harbouring life will be low. Yet, this doesn’t take anything away from the excitement of wondering whether we will eventually find life outside our Solar System.