[Artwork depicting a gas giant exoplanet with a gas giant exomoon. Credit: Shutterstock / Jurik Peter]
In a paper just published on the astronomy preprint server called arXiv, a group of astronomers has made an astonishing claim: They have found evidence of the possible existence of an exomoon, a moon orbiting a planet orbiting another star. If true, this will be the first moon orbiting an exoplanet ever discovered!
However, I want to be really, really clear here: The evidence is very interesting, and I might even use the word compelling. But it’s not conclusive, and certainly not confirmed. Importantly, the paper has not yet been peer-reviewed, either (it was released early because news of upcoming observations leaked, and the authors wanted to get ahead of any news stories that might be sensationalized; normally, I wouldn’t write about a non-peer-reviewed paper, but I agree with them, and hopefully this will curtail inaccurate coverage). Assuming it passes peer review, what they have here is evidence, which means it needs to be examined carefully, and follow-up observations must be made to further investigate it. If it pans out, it’s a major discovery, and a very exciting one. But please keep in mind the preliminary nature of this while reading.
The exomoon, if it exists, is orbiting an exoplanet named Kepler-1625b, which itself is orbiting a star called Kepler-1625 (and so, if the moon is confirmed it will be called Kepler-1625b-I). The star is similar to the Sun, with about the same mass, though 1.8 times the Sun’s size. This indicates it’s old, and may be starting to swell into a red giant. It also means the star has a low density, which turns out to be important (more on that below). The star is about 4,000 light years from Earth, which makes it apparently pretty dim.
The planet is a gas giant, about the size of Jupiter but with ten times its mass, and takes just under 290 days to orbit the star once. It was found in 2016 using the Kepler spacecraft, designed to look for exoplanets. For several years, Kepler stared at one spot in the sky, looking at the light from 150,000 stars. If a planet orbits its star edge-on as seen from Earth, then every time the planet passes in front of the star, we see a transit, a mini-eclipse. The light from the star dims a bit, and does so once every orbit, revealing the presence of the planet and the length of its year. Not only that, but the amount the light dims also tells us the size of the planet (a bigger planet blocks more light).
If a planet has a moon or moons, they, too, will likely pass in front of the star, dimming it. This is an extremely tricky observation to make, because moons are smaller than planets, and the amount of dimming is very tiny indeed. Attempts to look for exomoons have been tried since exoplanets were first found in the 1990s.
In this case, the astronomers looked at over 6000 individual transits from 284 different exoplanets, and tried to fit them using a physical model of what it would look like if a planet plus a moon transited their host star. But it’s not that simple! You have to try a lot of different combinations of moon sizes, planet sizes, moon orbit sizes, and so on. A whole lot: In the end, each transit was fit with millions of combinations of different physical models!
In almost all the cases, they didn’t find anything; statistically speaking, the transits looked just like lone planets crossing the faces of their host stars. But in one case, they found a transit that looked very much like it was a planet plus a moon. And that was Kepler-1625b.
The problem is, the data are a bit noisy, so it’s not possible to be 100% sure that’s what’s being seen in the observations. Also, because of its relatively long orbit, only three transits were seen for Kepler-1625b. But the data really are interesting.
Normally, a transit is smooth and symmetric except for statistical noise. The start of the dip and the end should look very nearly like mirror images of each other. But that’s not what they saw.
In the first transit, the best model fit shows a small dip preceding the main one, and then a sudden jump in brightness in the middle of the transit. The middle one shows a sudden dip in the middle and a wiggle at the end, and the third shows dips preceding and following the main dip. If the main dip is the exoplanet, those other dips could be caused by a moon!
These transit graphs are why I say the evidence is compelling. The astronomers looked at other possible reasons for them, including instrumental problems, starspots (like sunspots but on the star Kepler-1625), and more. Nothing they found was more likely than the existence of an exomoon. Interestingly, they considered the planet might have a ring system like Saturn’s, but that should produce symmetric dips on either side of the transit, which isn’t seen in all three transits. There are physical ways a ring could do that, but they’re very unlikely. A moon is a better guess.
Assuming that’s what’s causing these extra dips, Kepler-1625b-I is pretty big: Roughly the size of Neptune! It would be orbiting the planet at very roughly 2.5 million kilometers out. That’s a long way, but consider that Jupiter has a moon, Callisto, that orbits it at a distance of almost 2 million km. Since Kepler-1625b has more mass, it could hold on to a big moon at a larger orbital distance.
The size of the moon (again, if it exists!) is interesting, too. No moon anywhere that big exists in our solar system and, in fact, physical models of how moons form show you can’t form one that size. But that’s not necessarily a problem! Those same models predict the Earth shouldn’t have a moon as big as our Moon, either. But the model assumes the moon forms with the planet, at the same time, and ours is more likely the result of a huge collision that occurred after the Earth formed. Also, it’s possible that a massive planet could capture a big moon — we know Neptune’s moon Triton is a captured object, as are several moons of Saturn and Jupiter.
Another bit I found very interesting: If a moon orbits a planet too far out, the gravity of the star can destabilize the orbit. The moon has to be close enough to the planet for the planet’s gravity to dominate, and this distance can be calculated mathematically. It’s called the Hill sphere, and it depends on the planet’s and star’s density, and the planet’s distance from the star.
At first, it was thought that the star Kepler-1625 was much like the Sun. That was a problem, because a star as dense as the Sun would quickly destabilize an exomoon around Kepler-1625b. But updates to the data show the star is actually bigger than first supposed, possibly on its way to becoming a red giant, as I mentioned earlier. That means its density is lower, and in fact the moon should be stable over billions of years.
So, after all this, how can we find out if it really exists or not? The best way is to do follow-up observations with a big telescope to carefully measure the star’s light before, during, and after a transit of the exoplanet. And that’s just what the team is doing: They have Hubble observations planned for October, during a predicted transit. Given what they know, they’ve been able to predict what the transit graph shape should look like if the moon exists.
If the data are consistent with that, well then, that’ll be interesting, won’t it?
There have been a handful of other exomoon claims made in the past, but like this one, they remain unconfirmed. Given our own solar system, where most of the planets have moons, and even many asteroids and Kuiper Belt Objects do as well, it seems overwhelmingly likely that exoplanets will too. And that’s fine, but we won’t know for sure until we find one. Interestingly, there’s a search on right now for potential moons orbiting the exoplanet Beta Pic b, and if any exist they may very well be found.
This is so cool! We’re right on the edge of a new kind of astronomical endeavor. Once we find one of these exomoons we’ll find more, and they’ll be incredibly useful in helping us understand the planets they orbit.
Of course, that’s still in the future. But maybe not so far in the future.
My thanks to David Kipping, one of the paper authors, for a helpful conversation on this.2
Hide Related Posts & Comments
Listicle Display TypeDefault
Show the Media Gallery title
Video Hero Autoplay
Show on Hero
Sidetracks is a collaborative project featuring various essays, videos, reviews, or other Internet content that we want to share with each other. All past and current links for the Sidetracks project can be found in our Sidetracks tag. For more links and commentary you can follow us on Twitter, Tumblr. You can also support us on Patreon.
( Read more... )
In 2012, a wooden box was exposed by melting glacier ice of the Lötschenpass, 2650 meters above sea level in the Bernese Alps. Round and about eight inches in diameter, the unusual box was made of three different kinds of wood: pine for the floor, willow for the curved side and spliced larch boughs for the seams joining floor to side. Radiocarbon testing found the box dates to the early Bronze Age, about 4,000 years ago.
The ice that preserved the wooden box for four millennia also preserved traces of its contents. An international team of researchers analyzed the residue expecting to find milk remnants, perhaps all that was left of a porridge type food. Samples of the residue were subjected to lipid and protein analysis. Researchers examined the samples using microscopic and molecular analysis to identify any lipids and gas chromatography mass spectrometry for the proteins, a combination of techniques commonly used to identify residue in ancient and prehistoric ceramic vessels which survive in far greater numbers than wooden ones.
The results were surprising. Instead of milk remnants, the team found alkylresorcinols, indicators of the presence of whole grains.
Dr André Colonese, from BioArCh, Department of Archaeology, University of York, said : “We didn’t find any evidence of milk, but we found these phenolic lipids, which have never been reported before in an archaeological artefact, but are abundant in the bran of wheat and rye cereals and considered biomarkers of wholegrain intake in nutritional studies”.
“This is an extraordinary discovery if you consider that of all domesticated plants, wheat is the most widely grown crop in the world and the most important food grain source for humans, lying at the core of many contemporary culinary traditions.
“One of the greatest challenges of lipid analysis in archaeology has been finding biomarkers for plants, there are only a few and they do not preserve very well in ancient artefacts. You can imagine the relevance of this study as we have now a new tool for tracking early culinary use of cereal grains, it really is very exciting. The next step is to look for them in ceramic artefacts,” Dr Colonese added.
If phenolic lipids can be identified in ceramic vessels as well, it opens up the possibility of tracing the use and spread of cereals at the dawn of agriculture, information that is currently non-existent.
Researchers can’t tell at this point how the wheat cultivars made their way into the Swiss Alps. Some of the valleys in the area are known to have been inhabited during the Bronze Age, and grave goods have been discovered in burials in the neighboring canton of Valais that were imports from north and south of the mountains. The Lötschenpass may have been part of a trade route linking the Bernese Highlands to the Valais. Or it may not have anything to do with trade, just a box lunch packed by a lone hiker on a hunt or a drover pasturing cattle at higher altitudes than archaeologists realized were being used for grazing during this period.
Dr Francesco Carrer, from Newcastle University, said: “This evidence sheds new light on life in prehistoric alpine communities, and on their relationship with the extreme high altitudes. People travelling across the alpine passes were carrying food for their journey, like current hikers do. This new research contributed to understanding which food they considered the most suitable for their trips across the Alps.”
The study on the identification of cereals in the Bronze Age box has been published in Scientific Reports and can be read here.
He also took a dead bee home to look at under his microscope so expect potential photos of a dead bee in extreme closeup if we can work out how to take pictures through the microscope.
So…the marathon was good, especially in retrospect! Although honestly it wasn’t that bad even while I was running it. Definitely difficult, but not the hardest thing I’ve ever done — anything that lacks camel spiders and desert heat is automatically less difficult than anything that doesn’t. (No, Greg, I am not still thinking about the Marathon des Sables. Much. Don’t worry.)
But there are other ultramarathons with far lower risk of death… This one for instance.
I don’t know if it’s reasonable to except to be able to do that by October though, haven’t read up on it at all. Might be better to wait till next year, but we’ll see.
In other news, Roger Federer won Wimbledon again and all is right with the world. And my lovely husband bought me the limited edition T-shirt. Love it, and him.
(Greg's cranky because I'm threatening to sleep in it. Not sure if that's because he'd rather I didn't wear a shirt at all or if it's because he feels he can't compete with eight Wimbledon titles.)
This is also a weekly check-in! You do not have to check in, of course, but if you would like to comment on the last week, feel free!
Deadlines! I always offer to give deadlines and I mean it! The few times I've given deadlines to people, I've put a sticky note up on the wall by my desk and done a couple PMs as reminders. Other options include a sticky 'deadlines!' post on the community if members would be comfortable with that. (Or any combination of things...)
Do you have something you think you'd be more motivated to work on if you had a deadline for it?
If so, mention it in your comment, when you'd like your deadline to be (or I can pick something), and how you'd prefer it to be administered (community sticky, private PMs/sticky note, other, all of the above?), etc. There would, of course, be no penalty or guilt if the deadline doesn't happen. It's a hectic time of year for a lot of people and I only want to offer gentle nudges in the rear, not stress.
Silencing The Hillary Clinton Supporter: we've heard everything about the Trump supporters - to the point where mainstream media has been trying to 'humanise' right wing white supremacists, but nothing about the people who mostly supported Hillary - their hopes, their dreams, and what they lost when Trump was elected.
Brandon Hatmaker on Colin Kaepernick: Brandon Hatmaker is the husband (presumably) of Jen Hatmaker, an American Christian who spoke out in favour of LGBT in the church and had her books dropped from sale by one of the biggest Evangelical publishers in the US (and probably the world).
That Which Google Has Named Evil...: By co-opting a word with moral meaning to describe the functional impediment of technology without any specific morality attached, Google has effectively reframed the context of 'good' and 'evil' so that Google is God - the arbiter of what is right and wrong.
A Woman, Explaining Things: Yeah, you've probably seen this, but it's still good.
First They Came For...: New York Times, which means you might not be able to read it. (I saved it in Instapaper, which takes the page data and strips it down to the text and key images.)
This has come as a great shock and demoralizer to many Americans, not necessarily because they didn’t think Trump was capable of such depravity, but because they simply were unprepared for the daily reality of living a nightmare.Some things get better, many things get worse.
There is an enduring expectation, particularly among American liberals, that progress in this society should move inexorably toward more openness, honesty and equality. But even the historical record doesn’t support that expectation.
Australia has had an interesting week of governmental resignations (which everyone else would have missed while That Orange Guy was tweeting away).
Two Greens Senators and a Liberal (conservative party) Senator have had to resign because it turns out they have dual citizenship, which isn't allowed for serving members of Parliament. Another Liberal Senator no longer has a dual citizenship, but was only notified that he'd been de-citizened from the other country five months after the election that raised him to his position.
And, of course, he was one of the loudest voices criticising the Greens senators for getting it wrong.
I am done with microaggressions, even the unintentional ones.
No, you don’t get to ask me what’s my background and then say that yours is “Australian”. Mine is Australian. My mother is an Australian immigrant. My father is an Australian born. I am an Australian born.
I am an Australian-born Australian.
I am no more an immigrant than any white person in this damn country and I am going to FIGHT this definition all the way, calling people racist outright if necessary.
2. The "New Beginnings" playlist that heresluck made for me last year, to which I am listening even now.
3. Setting a pretty Shabbat table for tomorrow night.
4. The many excellent things that have been recommended to me in the last 24 hours! I devoured The Dream-Quest of Vellitt Boe (a truly lovely novella) last night, and am now beginning to read Too Fat, Too Slutty, Too Loud: The Rise and Reign of the Unruly Woman, which, um, yeah.
5. I'm gonna pour myself a glass of pink wine, because it's wine o'clock, y'all.
Over the last decade, Orbit US, an imprint of Hachette Book Group, has quickly established itself as one of the premiere publishers of science fiction and fantasy, and a reliable source for everything from innovative works of science fiction to blockbuster epic fantasies. To celebrate the milestone, a selection of landmark Orbit titles is currently available on Nook for just $2.99 each, but we wanted to do more than point you toward some great titles, so we asked Orbit’s publisher, Tim Holman, to share a bit of history. Below his comments, you’ll find a timeline of key dates in Orbit’s history.
Comment with the username you'll be using to rec and the category you want, choosing a category from the list below or selecting a more rare category that has been used in the past. If you want to rec a category that is not on the list below or in the community memories, feel free to ask. Remember that you may volunteer for a category that isn't listed.
By signing up, you are committing yourself to reccing at least two (preferably four) stories in that category during the month of August. July reccers may only sign up for next month after posting their minimum two recs for this month.
Please note that we are no longer asking reccers to check the memories to avoid reccing a story more than once. If you have a good fic to rec, go for it! The FAQ and rec template, with detailed instructions, can be found here.
You must be a member of stargateficrec in order to post, so if you're a new reccer, be sure to join the community.
If you wish to rec at the comm on LJ this month, go here.
( categories below the cut )
Remember: first come, first claimed.
I recently wrote about citizen scientists (people who are enthusiastic about science but who may not have professional scientific training) combing through NASA data and hitting pay dirt: They found a brown dwarf just a little over a hundred light-years away, one that had been missed by previous data searches.
It turns out there may be a lot more to find. And by a lot more, I mean A LOT MORE. Scientists have recently found that there could be as many as one hundred billion brown dwarfs in our galaxy, half as many as there are stars!
Brown dwarfs are funny objects. They’re more massive than planets, but lack the mass needed to squeeze hydrogen in their cores hard enough to get it to fuse into helium. That’s what makes a star a star: the ability to stably fuse one element into another. The definitions get complicated, because nature isn’t as fussy about having clear boundaries between one type of object from another as humans are, but in the end brown dwarfs occupy that space between planets and stars, similar to but distinct from both.
They’re their own thing. And we didn’t even know they existed until 1995, when the first, Teide 1, was discovered. They’re incredibly faint in visible light (the kind of light we see), and even in infrared, where they give off most of their energy, they’re not exactly beacons. But they started turning up in observations made by telescopes equipped to look in the infrared, and now we know of a few thousand.
The thing is, the ones we see are perforce nearby. More than a thousand light-years away or so, they fade to invisibility. That may seem like a lot, but the Milky Way galaxy is one hundred thousand light-years across! We’re only seeing brown dwarfs locally, so it’s hard to get good statistics on them galactically.
But there’s a way around that. The thing to do is look where you know there should be some ... like, say, a star cluster. These are groups of hundreds or thousands of stars, all bound together by their own gravity. Typically, the stars were all born around the same time from a cloud of gas, and that’s a huge advantage: As stars age they change color, and so by measuring their colors you can get the age of the cluster.
That’s important, because the same thing happens with young brown dwarfs, too. Their color depends on their mass — a more massive object is hotter, which makes it bluer— so if you know the color and age of a brown dwarf, you can determine its mass*. That helps you distinguish it from a planet or a star.
And a team of astronomers did just that. They looked at several star clusters that were close enough to Earth that brown dwarfs are visible. Then they basically counted up what they saw, measured the colors, and figured out how many of the objects were stars and how many were brown dwarfs.
What they found was that about half the objects in the clusters were brown dwarfs. Extrapolating that to the galaxy at large, there could be 25 – 100 billion such objects in the Milky Way galaxy alone.
This conclusion was already hinted at by previous stellar cluster surveys, but this one found that the result stayed the same across a variety of different cluster types. Some had more stars packed more tightly in them (which can affect how stars are born), and some had a lot of very massive stars, which can also affect the environment around them.
None of this appears to matter. Clusters make about two stars for every brown dwarf. And that means that our galaxy is littered with them.
This makes me very happy. I really like brown dwarfs; they’re fascinating objects and, once upon a time, I worked on Hubble observations of one of the two first brown dwarfs ever discovered, Gliese 229B. It was fascinating to see the spectra, revealing the presence of things like cesium and water vapor in its atmosphere. Water vapor: steam! I was used to observing stars and other very hot objects, so to find something as mundane as good old water in Gliese 229B was truly weird to me at the time.
Also, much like planets orbiting other stars, we had suspected the existence of brown dwarfs for decades, but they were maddeningly elusive. Then, once one was found, more started showing up. Once we knew they were out there, and the best way to look for them, we started finding hundreds of them. Thousands.
This is such a wonderful allegory. We look up at the night sky and try to imagine what’s out there, and what we find out is that there are wonders beyond what we would have thought even a few years ago! And not just a few, but billions, hundreds of billions of new things to discover.
The more we look, the more we let our curiosity drive us, the more there is to find. That’s one of my favorite things about our Universe.
*As with everything in science, it’s actually more complicated than this. You actually have to measure the brown dwarf’s spectrum, basically dividing its light into hundreds or thousands of very narrow color ranges. Even then it’s a bit tricky. But that’s the idea.4