Now it makes sense! We can consider Jupiter Family Comets as a potential source for Earth's water. We also understand why there isn't much N2 or CO in 67P.A big thank you to my co-authors Jake Lustig-Yaeger, Adrienn Luspay-Kuti, Olivier Mousis, Stephen Fuselier, Dennis Bodewits & others 🔭🧪🧵end
Kathy Mandt (she/her)
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Planetary scientist dabbling in exoplanet atmospheres. Wannabe Ice Giants explorer.
If the spacecraft moved far enough away from the comet, there wasn’t any more ice on the dust and we could isolate the gas coming from the comet itself. Our results was a lower D/H, more like what we expected and closer to Earth's water!🔭🧪🧵12/n
Laboratory studies had discovered that HDO sticks to dust easily making the D/H of ice on dust much higher than the ice in the experiments. We made a simple model to explain how extended sources could make D/H higher near the spacecraft. 🧪🔭🧵11/n
Some of the dust doesn’t have time to lose all its ice before it is deposited back onto the nucleus in the north where it’s winter. That dust is “reactivated” and becomes and extended source again when the comet begins to approach the sun on its next orbit.🧪🔭🧵10/n
https://link.springer.com/article/10.1007/s11214-020-00662-1
https://link.springer.com/article/10.1007/s11214-020-00662-1
Dust-to-Gas and Refractory-to-Ice Mass Ratios of Comet 67P/Churyumov-Gerasimenko from Rosetta Observations - Space Science Reviews
This chapter reviews the estimates of the dust-to-gas and refractory-to-ice mass ratios derived from Rosetta measurements in the lost materials and the nucleus of 67P/Churyumov-Gerasimenko, respectively. First, the measurements by Rosetta instruments are described, as well as relevant characteristics of 67P. The complex picture of the activity of 67P, with its extreme North-South seasonal asymmetry, is presented. Individual estimates of the dust-to-gas and refractory-to-ice mass ratios are then presented and compared, showing wide ranges of plausible values. Rosetta’s wealth of information suggests that estimates of the dust-to-gas mass ratio made in cometary comae at a single point in time may not be fully representative of the refractory-to-ice mass ratio within the cometary nuclei being observed.
Other researchers had discovered that 67P has a seasonal dust cycle. When the comet is at perihelion, a bunch of water comes out of the southern hemisphere which is in summer. This lifts a lot of icy dust from the nucleus into the coma which is heated and becomes an “extended source” of water.🧪🔭🧵9/n
Our results showed a huge amount of variability over the mission! We started to look at what caused this variability and found an interesting relationship with the amount of dust near the spacecraft and with the age of the dust. 🧪🔭🧵8/n
Then I met Jake, an exoplanet scientist who had a great technique to isolate HDO! We analyzed ALL the data available. We needed the whole dataset because DFMS only measures the part of the coma right by the spacecraft and we wanted to know if D/H varied. 🔭🧪🧵7/n
Rosetta’s complete journey around the comet
DFMS was a super powerful mass spectrometer. It could almost isolate water with deuterium (HDO) from other species that have the same mass. But, figuring out how much HDO was in each measurement was really hard. Most people could only evaluate a few measurements at a time by hand! 🔭🧪🧵6/n
The first results from Rosetta had a really high D/H that required 67P to form far away from the Sun. This was confusing! #67P is different from other Jupiter family comets that have lower D/H ratios. It also didn't have a lot of CO and N2 ice, which form at really cold temperatures too.
Comets are made up of dust and water ice. One of the most valuable measurements we make in a comet is the amount of deuterium (D) compared to hydrogen (H) in the water, D/H. The D/H in water tells us at what temperature ice formed, and from that how far a comet formed from the Sun. 🔭🧪🧵4/n