Anders Johansen 🪨🌍🇺🇦

I really recommend this long read about Pakistan’s solar power boom.

Advertisement!:
PhD-summer school at the Globe Institute, UCPH 18-22 August.
From interstellar dust to habitable planets and the conditions for life.
Interdisciplinary lectures with perspectives from astronomy, cosmochemistry, geology, and astrobiology.
For more see: www.dust2dna.dk

“Sure we need to address global warming. But what about China?”

Meanwhile in Heidelberg. Europe waking up to seeing our closest ally now run by conspiracy theorists and their sycophants.

'@bot.astronomy.blue signup'

No. How do I do that?

Comments and questions welcome.

arxiv.org/abs/2502.10186

So the radius gap may be primordial and photoevaporation, in our view, plays mainly a role of actually filling in the gap region with planets completely or partially stripped of their gas envelope.

This gives these nice 'crocodile' plots where the radius gap is clearly visible out to 0.5 astronomical units (AU) or so.

In our paper we explore instead whether the gap is primordial, so that planets below the gap never accreted gas while planets above the gap did. Gas accretion is triggered in our model when the planets reach pebble isolation mass; the cooling then allows H2/He to be accreted.

The most accepted explanation for this gap is that planets above the gap accreted a thick atmosphere of H2/He from the protoplanetary disc while those below lost this atmosphere by XUV irradiation from the star (these are close-in planets in much warmer orbits than Earth).

The radius valley describes the lack of planets with radii around 1.5-2 times Earth's radius. Here a famous plot of the radius gap from Fulton et al. (2017).

Let's see how many astrophysicists are on this platform compared to the other one.

I want to advertise quickly a paper first-authored by my soon-finishing PhD student Jesper Nielsen, on the formation of the so-called radius valley for small exoplanets.

arxiv.org/abs/2502.10186

Pessimists sound clever.

Optimists change the world.

That brings back good memories of my postdoc years in Leiden. Thanks 🙏!

Comment on "Did the terrestrial planets of the Solar System form by pebble accretion?" Morbidelli, Kleine & Nimmo (2024) (MKN) recently published a critical analysis on whether the terrestrial planets in the Solar System formed by rapid pebble accretion or by the classical route of mult...

I published a rebuttal today in reaction to a recent claim that Earth did not form by pebble accretion. Our conclusion is that Earth likely formed by a combination of pebble accretion, large impactors and a giant impact. Questions and comments welcome.

arxiv.org/abs/2411.17043

Famous Star Hasn’t Formed Planets, and We Don’t Know Why The nearby star Vega, featured in the 1997 movie Contact, appears to have a smooth disk devoid of giant planets for reasons we can’t explain

Story in Scientific American about Vega’s planet-free debris disc. With quotes from me. I think it’s because of the low metallicity.

www.scientificamerican.com/article/famo...

NASA's Webb Findings Support Long-Proposed Process of Planet Formation

"Webb finally revealed the connection between water vapor in the inner disk and the drift of icy pebbles from the outer disk" said principal investigator Andrea Banzatti

webbtelescope.org/contents/new...

The formation of wide-orbit giant planets in protoplanetary disks... The presence of distant protoplanets could explain the observed gaps in dust emission in protoplanetary disks. Here we derive a novel analytical model to describe the temporal decay of the pebble...

Whoa, this new study by e.g. @astroandersj.bsky.social shows how you can rapidly form giant planets at wide orbits, avoiding immediate inward migration. This could potentially explain the large gaps in disks!
arxiv.org/abs/2311.04365

A great community note from that other site.

Tack för att ni följer.