In our solar system, Earth stands out as the only body covered in liquid water. But it wasn’t always like this. When the planet first formed, it didn’t have the huge oceans it does today. So, where did that water come from? One idea is that it came from icy asteroids raining down on us — but that doesn’t explain everything. So now, there’s another idea.
Research published this week in Nature Astronomy proposes that some of Earth’s water was created by the Sun — not by melting ice, but by turning minerals into water.
One of the more helpful things in solving Earth’s water mystery is the fact that not every water molecule is the same. The vast majority are tried and true H2O — two hydrogen atoms, plus an oxygen. But some water is called D2O, because it contains a heavier version of hydrogen called deuterium. ~ Instead of being made of a single proton, it’s also got a neutron in its nucleus. ~ And that’s where the mystery starts to come in. Scientists have found that the ratio of deuterium to hydrogen in Earth’s oceans doesn’t match the ratio in the water they think was delivered to Earth on icy asteroids billions of years ago. Or at least, it doesn’t match what they’ve seen in similar meteorites today.
That suggests the Earth may have had another source of water, or an additional one. And in this new paper, one team tried finding it by turning… to the Sun. See, the Sun doesn’t just emit light. It also sends off streams of charged particles, called the solar wind. The vast majority of these particles are lone protons, which are identical to hydrogen nuclei. And the key is, previous research has demonstrated that these protons can react with oxygen atoms in certain minerals to create water. Specifically, silicate minerals, which are found all over the place.
That water then gets trapped in the surrounding mineral structure. And since silicate minerals are so common, this process could happen in everything from interplanetary space dust to the Moon’s crust. So, this team hypothesized that this kind of deuterium-free water formed in dust grains or asteroids in space, and eventually crashed into Earth. But they also tested this idea. First, they first measured the abundance of water in a sample collected from the asteroid Itokawa. They looked at a single grain of a silicate mineral called olivine. And they confirmed that the grain had been enriched with H2O, likely thanks to the solar wind. Then, they did experiments on local olivine grains.
They exposed them to beams of hydrogen and deuterium nuclei, since deuterium is also found in the solar wind, although it’s way less common. And they found that olivine samples exposed to deuterium had extra D2O — a.k.a. deuterated water, or heavy water. Now, they didn’t make any H2O with the regular hydrogen beam, but that could be because hydrogen is really light, and it’s harder to get the reaction to work. Still, because bombarding olivine with deuterium made heavy water, the researchers concluded it’s likely that solar wind protons create regular water in space, too.
That said, there’s still a lot of uncertainty here — after all, they only studied a single piece of asteroid. But overall, this supports a new way Earth could have gotten some of its water — not just from icy rocks from the outer solar system, but also from an army of irradiated asteroids and space dust. Our next story also involves water… but it’s much farther from home. We’re going way out to the TRAPPIST-1 system – a collection of seven planets about 40 light-years away. Based on how close they are to their star, at least three of these planets could have liquid water on their surfaces. But if they do, they likely got their water much faster than Earth. At least, those are the results published last week in Nature Astronomy.
The paper mainly focused on how fragile this planetary system is. The TRAPPIST-1 planets we’ve detected orbit both really close to their star, but also to each other. They’d basically look like moons in each others’ skies.
The planets are also spaced at precise distances from each other. They’re in resonance, which means that the lengths of their years relate to one another. As an example, for every eight years on the planet TRAPPIST-1b, exactly five years pass on planet 1c. To get this special relationship, previous research has suggested that all the planets had to have formed farther away from their star within just a few million years — significantly faster than Earth. Then, they would have migrated inward while there was still a disk filled with smaller planet-making materials. And this disk would have guided the system into resonance. If that’s what happened, the TRAPPIST-1 system has been stuck in this arrangement for literally longer than Earth has existed. But it’s a super fragile one.
Like, if a space rock smashed into one of these planets with enough force, or if too many smaller rocks smashed into several of them over and over, the entire thing would break down. In fact, the astronomers behind this new paper calculated the maximum amount of stuff that could have smashed into these worlds without disrupting their orbital harmonies. According to their computer simulations, the TRAPPIST-1 planets couldn’t have been hit by more than a combined mass equivalent to Mercury over the past seven-ish billion years. And that brings us back to the planets’ water.
If these worlds couldn’t handle being bombarded by asteroids like Earth, where did their water come from? Well, there was a lot of uncertainty in these models, but the researchers found that even a little bombardment could have delivered an ocean’s worth of water, especially to the outer planets. Alternatively, if these worlds did form farther from their star, they may have started with a bunch of water in the first place.
And they may have been cool enough that all of their water didn’t boil away as they migrated toward their star. ~ To get a more detailed look, astronomers will have to wait for the ultra-powerful James Webb Space Telescope to come online. But the incredible news is, after years of delay, the telescope is finally scheduled to launch in less than a month! So it’s only a matter of time before we start getting data.