James Webb Space Telescope launching tomorrow (Christmas)!

[ahalpert]

james webb captures its first direct images of an exoplanet: https://blogs.nasa.gov/webb/2022/09/...distant-world/

also of note is this side-by-side comparison of the first photo taken of Jupiter and the latest by James Webb:

jupitercomparison.jpg
https://petapixel.com/2022/08/30/the...s-latest-shot/

[Doug Jensen]

I never expected they'd be able to see that much detail in an exoplanet. I'll bet it takes a lot of manipulation in post to bring it out.
The weird thing is that the article says the planet is 7-12 times the size of Jupiter, but I thought Jupiter was just a little below the mass threshold for becoming a star. The new planet must be made of different stuff or it wouldn't still be a planet at that size.

[ahalpert]

I never expected they'd be able to see that much detail in an exoplanet. I'll bet it takes a lot of manipulation in post to bring it out.
The weird thing is that the article says the planet is 7-12 times the size of Jupiter, but I thought Jupiter was just a little below the mass threshold for becoming a star. The new planet must be made of different stuff or it wouldn't still be a planet at that size.

I'm not sure. From what I'm reading, it seems that the core density matters as well as the mass. Of course, maybe the mass is just a smidgen too low to initiate fusion.

Modelling suggests that the upper limit for a planet mass, forming via core accretion, is less than 10 times the mass of Jupiter - just a few Jupiter masses shy of deuterium fusion.

https://www.google.com/amp/s/www.sci...ter-a-star/amp

I think that the process of star formation produces a denser object than the process of planet formation. From the same arricle:

Stars and planets, you see, are born through two very different mechanisms. Stars are born when a dense knot of material in an interstellar molecular cloud collapses under its own gravity - pouf! flomph! - spinning as it goes in a process called cloud collapse. As it spins, it spools in more material from the cloud around it into a stellar accretion disc.

As the mass - and therefore the gravity - grows, the core of the baby star is squeezed tighter and tighter, which causes it to grow hotter and hotter. Eventually it becomes so compressed and hot, the core ignites and thermonuclear fusion kicks off.

According to our understanding of star formation, once the star has finished accreting material, a whole lot of accretion disc is left over. This is what the planets are made of.

Astronomers think that, for gas giants like Jupiter, this process (called pebble accretion) starts with tiny chunks of icy rock and dust in the disc. As they orbit the baby star, these bits of material start to collide, sticking together with static electricity. Eventually, these growing clumps reach a large-enough size - around 10 Earth masses - that they can gravitationally attract more and more gas from the surrounding disc.

From that point, Jupiter gradually grew to its current mass - about 318 times the mass of Earth, and 0.001 times the mass of the Sun. Once it had slurped up all the material that was available to it - at quite a remove from the mass required for hydrogen fusion - it stopped growing.

So, Jupiter was never even close to growing massive enough to become a star. Jupiter has a similar composition to the Sun not because it was a 'failed star' but because it was born from the same cloud of molecular gas that gave birth to the Sun.

The sun is a bit denser than Jupiter despite the outward pressure caused by fusion which reduces its density. So, without fusion, I think it would be a lot denser than jupiter.

Jupiter’s average density is about 1.326 g/cc, while the Sun’s average density is 1.408 g/cc…so the Sun has a higher average density.

Both bodies have very similar composition, and since the Sun is much larger, the increase in gravitational compression should increase the Sun’s density far more than Jupiter’s, however, the Sun is generating a great deal of energy from nuclear fusion, so the radiative pressure reduces the Sun’s density, making them very close in density.

Answer to Is Jupiter more dense than the Sun? by David Goodman https://www.quora.com/Is-Jupiter-mor...et_type=answer

But I'm not positive about why this exoplanet isn't undergoing fusion, I'm just making inferences based on articles about Jupiter.

Another interesting note which I never learned or just forgot is that Jupiter is so massive that the sun orbits around a point between itself and Jupiter.

Jupiter is so big that the center of gravity of the sun and Jupiter is outside of sun. Although extremely close to the surface of the sun.

So the sun and Jupiter both orbit around their center of gravity which is also known as barycenter.

Barycenter is the center of mass of two or more bodies that orbit one another and is the point about which the bodies orbit.

Answer to Is it true that Jupiter is so large that it does not orbit around the sun? by Prerak Sharma https://www.quora.com/Is-it-true-tha...et_type=answer

It seems like the James Webb telescope has a tool for masking out the light from the star so that the planet can be seen, called a coronagraph (presumably because these tools were first used for imaging the sun's corona) but I can't find a picture of what its coronagraph actually looks like.

[ahalpert]

Wow. Webb's new photo of Uranus and its dust rings which I didn't know it had

Screenshot_20230406_151923_Gallery.jpg

Screenshot_20230406_151939_Chrome.jpg

https://petapixel.com/2023/04/06/web...and-its-rings/

[Paul F]

Is that a dynamic range test pattern around the planet?

[Doug Jensen]

I never expected they'd be able to see that much detail in an exoplanet. I'll bet it takes a lot of manipulation in post to bring it out.
The weird thing is that the article says the planet is 7-12 times the size of Jupiter, but I thought Jupiter was just a little below the mass threshold for becoming a star. The new planet must be made of different stuff or it wouldn't still be a planet at that size.

It's funny you'd revive this thread this week because I was reading a book last night called "Strange Universe", and here is a quote from the book: "Contrary to popular belief, Jupiter was never almost a star. Even if it had 50 times more mass, temperatures would be insufficient to ignite nuclear fusion in its core."

Good book, by the way, I highly recommend it.
https://www.publishersweekly.com/978-0-8050-7328-7

[ahalpert]

James Webb has detected possible signs of life on a planet 120 light years away.

The telescope detected a molecule called dimethyl sulfide (DMS) — which only living organisms can produce, at least here on Earth — on the planet, which is dubbed K2-18 b.

Researchers also identified methane and carbon dioxide in the planet's atmosphere, indicating it could be a "Hycean" planet, one which is covered in an ocean and has a hydrogen-rich atmosphere.

K2-18 b orbits its host star, a cool dwarf in the Leo constellation some 120 light years away, in the system's habitable zone, meaning that it technically receives enough radiation from the star for liquid water to exist on its surface...

But it's far too early to conclude that K2-18 b is teeming with life, and the researchers were quick caveat that more data is urgently needed.
''If confirmed, it would be a huge deal and I feel a responsibility to get this right if we are making such a big claim," team lead Nikku Madhusudhan, professor at the University of Cambridge, told the BBC.

Fortunately, more data is already on its way, courtesy of the JWST's MIRI (Mid-Infrared Instrument) spectrograph.

https://futurism.com/the-byte/james-...distant-planet