Save the atmosphere with a crash

1 · Weigh up a collision

Beginner

According to this study, what does a late giant impact usually do to a rocky planet's atmosphere?

It holds it more tightly than before It almost always strips it away It changes nothing

2 · Place a planet of 4 Earth masses

The authors fit the curve at which only 1% of planets lose their whole atmosphere: χ = 0.58 − 0.0188 (M/M⊕)^1.794, where χ is the impactor's mass divided by the final mass and M the starting mass, in Earth masses. Above the curve, planets almost always keep their primordial atmosphere.

Intermediate

For a planet starting at 4 Earth masses, at what value of χ does the curve sit?

About 0.24 About 0.58 About 0.35

3 · Test a planet of one Earth mass

In the model, the largest impactor brings at most half the final mass: χ ≤ 0.5. The curve for 1% total loss is still χ = 0.58 − 0.0188 (M/M⊕)^1.794.

Expert

For a planet starting at one Earth mass, which collision takes it above the curve?

An impactor of a tenth of the final mass None: it is safe without a collision No collision the model allows

4 · Predict a world where every planet is hit

In the main simulations, each planet has a 52, 63 or 74% chance (depending on the run) of a giant impact after the gas disc has gone. The authors run a control in which every planet suffers one.

Expert

What do they get in this control?

Too many bare super-Earths Too many planets keeping their hydrogen The two observed peaks, unchanged

Atmosphere saved

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