One of the difficulties of studying star and planetary formation has historically been the difficulty of confirming our hypotheses. As our understanding of the universe has expanded, our own theories have often come in for revision. We now know, based on the results of surveys like that of the Kepler telescope, that so-called “Hot Jupiters” — gas giants orbiting very close to their host stars — are fairly common, while our own solar system appears to be rather unusual in composition, in the location and distance between its planets, and even in the types of orbits those planets follow around the star.
It’s possible, of course, that the pendulum has swung in the opposite direction, and that our solar system only looks erroneous because the types of planets we can see around other stars tend to occur in systems very different from our own. But with more than 3,500 verified exoplanets, you’d expect to see at least a few that resembled us. So far, not much luck.
But despite the differences between our own solar system and the rest of the solar systems we can see, it looks like our theories of planetary formation are bang on track, thanks to new images that actually captured the planetary formation process around another star for the first time.
The image above shows the star PDS 70, 370 light-years from Earth, but the star has been blocked by a filter to allow us to observe the gas cloud around the star. Astronomers working on the European Very Large Telescope in Chile imaged PDS 70 because they had observed a gap in its protoplanetary disc, which typically implies an object large enough to be attracting material to itself.
That yellow-orange blur at the right-hand side of the image? That’s a baby planet in the process of coalescing.
Don’t let the relative image size fool you — PDS 70b is a gas giant several times the mass of Jupiter and takes roughly 120 years to make a single orbit around its sun. That puts it between Uranus (84 years) and Neptune (~165 years) relative to Earth planets. Its 22 AU distance from its home star also puts it between these two planets; Uranus is 18-20 AU from the Sun, while Neptune is ~30 AU away. With an estimated temperature of 1200K and a deep red tint, the planet is thought to still be hoovering up material from the dusty belt around the planet.
HL Tau, protoplanetary disk, as seen by ALMA
Combine this find with the first discovery of a forming star system, HL Tau, back in 2014, and it means we’ve now got confirmation that our theories on how stars and planets both coalesce out of gas and dust clouds are generally accurate. Obviously there’s still room for plenty of refinement, particularly given the uniqueness of our own solar system and the various models that have been proposed to explain it. There is, to be sure, much we still do not understand, including whether or not Jupiter once took a leisurely voyage across the solar system before being reversed by gravitational interactions with the other gas and ice giants.
But the more planets and stars we find in the earlier stages of formation, the greater the chances we’ll spy scenarios that relate more directly to our own solar system — possibly shedding clues on our own history in the process.