A couple of updates on the big news of last week. In case you missed it, a team of astronomers announced they had detected signs of a potential biosignature (chemicals indicating the presence of life) on an exoplanet called K2-18b, about 120 light-years from Earth. 

I was pretty skeptical, especially when the team leader, Nikku Madhusudhan, started making claims that I (and many, many other astronomers) felt were way beyond what the data were indicating. I was pretty clear that the data didn’t necessarily indicate the presence of those chemicals, and even if so they weren’t necessarily a sign of life.

I may have been too conservative. Some new research shows that their data may not even show a signal of anything at all!

In a nutshell, the Madhusudhan’s team used JWST to observe the planet K2-18b when it was in front of its star, when light from the star passes through its atmosphere on the way to Earth. Different molecules absorb light at different wavelengths, so by looking at where the light from the planet is dimmer you can, in principle, measure what chemicals are in its air. If you plot the brightness versus wavelength, you get a graph with wiggles in it, dips in the brightness called absorption lines. It’s those features the astronomers use to claim the presence of possible biosignatures.

Well, planetary scientist Jake Taylor examined the data in different way. He looked at the spectrum and fit it with Gaussian curves, meaning he took different mathematical functions with shapes similar to absorption lines and tried to match them to the data, to see if he could replicate the claims [link to journal paper].

The punchline is that when he did so, he found that the spectrum was statistically indistinguishable from a flat line. In other words, those dips may not even be real at all!

Ouch. This throws a bucket of very cold water on the entire claim made by the original team.

I talked about this with my friend Deborah Byrd on her EarthSky livestream, and I am plenty skeptical and critical of how this biosignature claim was initially handled:

NPR has an article with some more details, and quotes from Taylor. Incredibly, Madhusudhan replied to NPR to say, “there is nothing in this paper that worries me or seems relevant to the discussion about our result. I am only slightly surprised that the bar is so low for a rebuttal!”

This reply disappointed me. It’s possible the quotation doesn’t include details he might have given, but even so it still comes across as dismissive of the work of a fellow scientist.

And he already had at least one dismissively disparaging comment for a scientist asking about his results, and that plus his previous comments in the initial press release (which I wrote about in my newsletter article last week) really give me pause. A scientist needs to be at least somewhat removed from their results; not dispassionate or completely distanced, but enough so to be willing and able to greet any criticism honestly and openly. In my opinion, that’s not happening here. There’s been plenty of criticism, and Madhusudhan just seems to want to wave it away.

We’ve seen this sort of thing before with astronomers who make extraordinary claims based on less than extraordinary evidence, making headlines in the process. The important thing to pay attention to is not what the media say, but what other scientists say. And a lot of scientists have said the results by Madhusudhan and his team are nowhere near the claims they’re making. It’s the way to bet.

And now, after that unpleasantness, a unicorn chaser.

On April 24, 1990, the Space Shuttle Discovery carried Hubble Space Telescope into space.

To celebrate the 35^th anniversary of that day, NASA and the ESA have released four gorgeous images from Hubble. One shows Mars, another the planetary nebula NGC 2899, the third the Rosette Nebula, and the fourth the galaxy NGC 5335 (they also released another one last week of the astonishing Sombrero Galaxy).

I urge you to click that and look at all four, since they’re all spectacular. But here is the last one, NGC 5335, for your attention:

[Click here for the spectacular 4,000 x 4,000 pixel version!] 

NGC 5335 is about 200 million light-years away from us in the constellation Virgo. It’s a spiral galaxy, obviously, but a weird one.

For one thing, the arms aren’t terribly well defined like you see in many spirals. They’re fluffy, patchy, what astronomers call flocculent. Flocculence is an odd phenomenon and not well understood, though it may be due to stochastic self-propagating star formation. Does that clear things up? No? OK, the phrase means that somewhere in a galaxy some gas clouds form stars, and the massive stars born there can explode and trigger star formation in a nearby gas cloud, which forms massive stars that explode, etc. and so on und so weiter. The rotation of the galaxy shears those star birth sites away from each other, creating the patchy appearance.

NGC 5335 is a barred spiral, named after that elongated structure in the middle that makes it look like Darth Vader’s TIE fighter. Bars are pretty common — our Milky Way has one — and they come in many shapes and sizes. This one is very prominent!

Stars in a galaxy orbit the center similar to the way planets orbit the Sun, but in the solar system the Sun, sitting in the center, dominates the mass. In a galaxy the stars themselves provide the mass, and they’re distributed throughout the disk (dark matter is there too, but also spread out). This means the way things interact is different. Instabilities in the disk can trigger all sorts of structures, including a bar, where the stars and gas and dust all seem to fall into that odd shape.

This can also funnel gas to the galaxy center where stars can form from it, though I suspect the birthrate is low. Massive stars are bright and blue, but don’t live long. That’s why the arms are blue; that’s where the stars are born. Disk galaxy centers tend to be yellowish or red, because star formation ceases there long ago, and red stars live longer than blue ones. All that are left are those redder ones. We don’t see a lot of blue in the galactic center, so there can’t be too much star formation there.

Anyway, I began my PhD work two weeks before Hubble launched in 1990, and spent several years working with images from it of a supernova. After that I worked on a camera, STIS, that was placed onboard Hubble in 1997. I spent about a decade total with the observatory, and it’s always nice to have an anniversary come up and be able to share more of the Universe’s beauty as pictured by it.

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!