Life on planet Earth has originated from one fundamental element: water. Evidence shows that water on our planet was present at least 4.4 billion years ago, just after the Earth’s formation. However, scientists still debate whether water formed with it or arrived later from somewhere else. Trying to answer questions like this, astronomers are studying distant solar systems with characteristics similar to the one we live in. In particular, astronomers seem to have found something interesting about the PDS 70 stellar system, thanks to the James Webb Telescope.
🆕 Webb’s #MIRI instrument has detected water vapour in the inner disc of the system PDS 70. ♨ This is the first detection of water in the terrestrial region of a disc already known to host two or more protoplanets. Read more: https://t.co/4Dg9pYG2qN or 🧵👇 pic.twitter.com/WGljCGTpkc— ESA Webb Telescope (@ESA_Webb) July 24, 2023
PDS 70 has been chosen as a benchmark for water research due to the directly confirmed presence of two accreting protoplanets (PDS 70b and PDS 70c) orbiting inside an annular gap between an inner and outer disk. The rifle for this hunt was the Mid InfraRed Instrument (MIRI) on board the James Webb Space Telescope (JWST) able to detect wavelengths between 5 to 28.3 microns.
The MIRI spectrum of PDS 70 shows the presence of silicate dust grains (mainly enstatite and forsterite, often found in meteorites) and water. The graph in the picture shows that what the James Webb observed (in white) coincides with what is expected to be the water vapor model (in blue).
The exciting thing about this discovery is that water is located less than 160 million km from the star, in the inner disc, a region of space where rocky planets usually form. Here dust and gas have mainly two fates: being blown away by the stellar radiation or growing into larger objects. Since inside discs around stars like PDS 70 astronomers never found water, they suspect this is because the first of the two options is the most probable. However, in this region, scientists see a group of raw materials that could aggregate to form a planet that would have water available since its birth. Moreover, precisely these materials are shielding water from radiation.
Where does the water come from?
Astronomers have put forward two hypotheses. The first one expects the formation of water in situ from a chemical reaction involving hydrogen, oxygen and/or hydroxyl group (OH). The second one, instead, expects the water to be transported by ice-coated dust particles from the outer to the inner disk where it turns into vapor. Nevertheless, the presence of CO2 and the large gap the dust would have to cross make this last option less likely.
This first analysis proves that the inner disk of PDS 70 is rich in water. Scientists, after this discovery, believe that the presence of water in the terrestrial planet-forming zone is not as rare as thought and, to prove it, further observation will be done around other stars. Are we close to finding out how water got to our planet?