Our Solar System was born in chaos. Collisions shaped and built the Earth and the other planets, and even delivered the building blocks of life. Without things smashing into each other, we might not be here.
Thankfully, most of the collisions are in the past, and now our Solar System is a relatively calm place. But frequent collisions still occur in other younger solar systems, and astronomers can see the aftermath.
Although the Arecibo radio telescope is no more, it continues to deliver scientific discoveries. There is a wealth of Arecibo data astronomers continue to mine for new discoveries, and one of them is thanks to an astronomical technique known as planetary radar.
Uranus and Neptune are similar planets in many ways. Both are ice giant worlds, both have atmospheres rich in methane, and both have a bluish color. But while Uranus has a pale blue-green hue, Neptune has a deep blue color. But why? Why would two planets so similar in size and composition appear so different? According to a recent study, the answer lies in their aerosols.
The Moon has orbited Earth since the Solar System’s early days. Anyone who’s ever spent time at the ocean can’t fail to notice the Moon’s effect. The Moon drives the tides even in the world’s most remote inlets and bays. And tides may be vital to life’s emergence.
But if Earth were more massive, the Moon may never have become what it is now. Instead, it would be much smaller. Tides would be much weaker, and life may not have emerged the way it did.
Some planets orbit their stars so closely that they have extremely high surface temperatures and extremely rapid orbits. Most of the ones astronomers have found are Hot Jupiters— planets in the size range of Jupiter and with similar compositions as Jupiter. Their size and proximity to their star make them easier to spot using the transit method.
But there’s another type of planet that also orbits very close to their stars and has extremely high surface temperatures. They’re small, rocky, and they orbit their star in less than 24 hours. They’re called ultra-short-period (USP) planets and TESS found one that orbits its star in only eight hours.
And the planet’s density is almost equivalent to pure iron.
If we had to rely solely on spacecraft to learn about the outer planets, we wouldn’t be making great progress. It takes a massive effort to get a spacecraft to the outer Solar System. But thanks to the Hubble Space Telescope, we can keep tabs on the gas giants without leaving Earth’s orbit.
Not that long ago,, astronomers weren’t sure that exoplanets even existed. Now we know that there are thousands of them and that most stars probably harbour exoplanets. There could be hundreds of billions of exoplanets in the Milky Way, by some estimates. So there’s no reason to think that stars in other galaxies don’t host planets.
But to find one of those planets in another galaxy? That is a significant scientific achievement.
What makes a planet a planet? The answer turns out to be rather contentious. The official definition of a planet, as defined by the International Astronomical Union (IAU) is that a planet must satisfy three conditions:
It must orbit the Sun.
It must be in hydrostatic equilibrium.
It must have cleared its orbital neighborhood.
By this definition there are just eight planets in our solar system, most notably excluding Pluto. This has stirred all manner of controversy, even among astronomers. Several alternative definitions have been proposed, but a new study argues we should look to history for the solution.
The search for potentially habitable planets is focused on exoplanets—planets orbiting other stars—for good reason. The only planet we know of with life is Earth and sunlight fuels life here. But some estimates say there are many more rogue planets roaming through space, not bound to or warmed by any star.