Archive for the ‘exoplanets’ Category
stuff about the Nancy Grace Roman space telescope
Roman in the purple haze
So I’m at a loss to find anything to write about, as often happens, as there’s nothing I’m really knowledgeable about, and global politics is generally too awful to take seriously, but I must needs keep writing, for what else am I good for?
This morning I’ve been listening to people at NASA or is it Goddard talking to informed members of the public about the Nancy Grace Roman Space Telescope, aka Roman, which I’ve vaguely heard about before, but this was all very exciting talk about it being launched around September, way ahead of schedule and under budget. So look out, dark matter, dark energy and the multiverse, here we come.
I’ve recently heard people I know – not the most sciencey people on the planet – going on about the Artemis missions as ‘been, there, done that’ and a money-wasting ‘nothingburger’, but given some of the shite happening here on Earth, one can’t help indulging the fantasy of getting away from it all. And I couldn’t help feeling a pang of envy for the Goddard people in their happy bubble of space enterprise. Beam me up, I say – or is it down?…
But the Roman really does seem a fantastical piece of machinery, worth exploring. First, though, who was Nancy Grace Roman? Well, sadly she died on Christmas Day, 2018 – a bit of a downer for the family, but then she was 93. She was an astronomer, and NASA’s chief of astronomy in the 70s, an important figure in planning the Hubble Space telescope, an educator, and an advocate for sciencey women, so, what with the Vera Rubin and the Just Wonderful Space Telescope (didn’t catch on, sadly), women are creeping closer to space dominance. The news conference I listened to was full of optimistic excitement and pride. The launch is set for September, for a Sun-Earth orbit at Lagrange point 2.
So, onto Lagrange points, which I used to understand, I think. They’re points of gravitational equilibrium between two massive orbiting bodies, in this case the earth and the sun. They’re a place of balanced forces, perfect for a relatively small body such as a spaceship, or a space telescope, to make a stable home. There are five Lagrange points in the orbital plane of the earth-sun system, which is standard for any such large body system. So, getting out of the earth’s atmosphere has obvious advantages for clear viewing, what with Rayleigh scattering, ozone absorbing UV light, and other problems.
The Roman is particularly an advance on the Hubble, as they’re similar types, with the Roman having a much wider field of view. And then there’s the Vera Rubin, which I’m sure I’ll get round to (this is all just a self-education vid).
But now for the coronagraph. From Wikipedia:
A coronagraph is a telescopic attachment designed to block out the direct light from a star or other bright object so that nearby objects – which otherwise would be hidden in the object’s bright glare – can be resolved.
I’m listening to/watching a video from three years ago featuring a Dr Vanessa Bailey, who is clearly very excited and also very knowledgeable about the Roman and its coronagraph – doubtless even more excited now as the launch date has been put forward to September this year, instead of 2017. It gets very technical for a know-nothing like me, but I intend to watch it more than once as well as reading up on coronagraphs and the Roman on Wikipedia etc. I feel something coming on as I try to process this stuff, a real sense of excitement, not so much about weird physics, massless particles, strangeness and charm, and the multiverse, but habitable planets, and exoplanets in general. No doubt Roman will be charged with duties other than exploring exoplanets, but the expansion of our exoplanet discoveries since the nineties has excited me more than anything else in astronomy.
So I’ve given Wiki’s brief description of a coronagraph above, and it’s clear from that description that coronagraphs will be key to locating and exploring exoplanets (6,273 confirmed as of April 23 2026, and many more yet to be confirmed, and AI never lies). Apparently the Roman will be equipped with a ‘next generation’ coronagraph – essentially there are two types, solar and stellar – and with the Roman it’s about stellar coronagraphs, which are intended to block or reduce light from all stars or bright objects other than the sun. The telescope itself is similar in size to Hubble, but Dr Bailey points out that Roman’s field of view will be such that it will be able to do ‘in one shot’ what would require dozens of shots from Hubble, and this wide field will help with exploring dark matter and dark energy. The coronagraph will have a one hundred-fold greater sensitivity than that of Hubble.
We get into heavy detail at this point, Fraser Cain, the interviewer, being way more nerdy – I mean expert – about this stuff than me, what with F-numbers (reference below), which have much to do with field-of-view and clarity, and gravitational lensing and its possible connection with dark matter, and other distortions.
So, the coronagraph. The whole purpose of this one is as a ‘technology demonstrator’. To quote Dr Bailey:
by the 2040s, NASA wants to be imaging Earth-like planets around nearby Sun-like stars to search for life – I mean, we’re talking single-pixel, very fuzzy images, we’re not talking continents and clouds, but even to be able to detect Earth-like planets at all, you’re trying to find something that’s ten billion times fainter than its host star – incredibly close at least in terms of its angular separation. What Hubble can do, in terms of its coronagraph, is on the order of a million times fainter – which is phenomenal, it lets us see young hot glowing Jupiters, that are still emitting plenty of light from the heat of their formation process, but that’s nowhere near what we need for those ‘exo-Earths’. So the Roman coronagraph is going to be an intermediate generation of instrumentation – we hope we’ll definitely achieve at least 10 million to one detection limits for a planet that’s 10 million times fainter than its star – our goal is to do 100 million to one, closer to a billion to one…
All of which sounds pretty exciting to me, except that I’ll be turning 90 around the middle of the 2040s – gotta get that little cough under control. Dr Bailey continued to detail aspects of the coronagraph which go way beyond my comprehension, having only looked through a basic little telescope once or twice in my life, a most pleasant memory. Apparently the Roman coronagraph will have around a hundred times the sensitivity of Hubble, which will presumably lead to far more habitable zone planets being detected and surveyed for any interesting anomalies or signs of – I dare not speak its name. and of course there will be other possibilities relating to dark matter and other mysteries. For example measuring the shapes and perhaps the more detailed activities of galaxies may throw more light onto dark matter, so to speak.
And of course I remember those first exoplanet discoveries in the 1990s, and the sudden knowledge, for me at least, that every one of the zillions of stars out there was a solar system. I’m not sure if Hubble was essential to those first discoveries, but it’s probable. A NASA website on Hubble is fascinating on this, so I’ll just quote:
For a long time, scientists thought that other planetary systems were likely to resemble our own. But humanity was in for an eye-opening revelation about what constituted a run-of-the-mill planetary system. The first exoplanet discovered was a “hot Jupiter,” or a Jupiter-like gas giant orbiting astoundingly close to its star ― only 5 million miles (8 million km). That’s closer than Mercury is to our Sun.
The variety of new types of planets that poured in were astounding. In addition to many hot Jupiters, astronomers found:
- Super-Earths: Rocky planets more massive than Earth, but lighter than Neptune
- Hot Neptunes: Neptune-size planets in tight orbits around their stars
- Mini-Neptunes (or sub-Neptunes): Roughly Neptune-size planets thought to have solid inner cores and dense helium-hydrogen atmospheres
- Ultra-hot Jupiters: Jupiter-like gas giant planets orbiting so close to their stars that their temperatures exceed 3,000 degrees Fahrenheit, hot to vaporize most metals
- Super Puffs: Young planets with the density of cotton candy. Their hydrogen/helium atmospheres are so bloated they are nearly the size of Jupiter, but their mass is only several times that of Earth
So, that’s enough excitement for now, and it’s only the beginning. This is something I hope to follow, if health allows.
References
NASA News Conference: Nancy Grace Roman Space Telescope is Complete
https://en.wikipedia.org/wiki/Nancy_Grace_Roman_Space_Telescope
How Nancy Grace Roman’s Coronagraph Will Revolutionise Planet Hunting (Fraser Cain interview with Dr Vanessa Bailey)
water on Earth – no problemo
So, as described in my last post, H2O in its various forms is plentiful in our solar system as well as beyond it. But, being more or less scientifically illiterate – despite decades of reading stuff on science – I can’t quite work out how liquid water is so abundant on the Earth’s surface. The story has long been told of water-iced asteroids in the time of the heavy bombardment being responsible, with the major proof being that these carbonaceous chondrite asteroids have, or had, the same signature of heavy (deuterium-rich) water as the water we find on Earth. While this seems a strong argument to me, how did the Earth manage to hold on to that water during those super-heated days?
I’ve looked at this in a previous post, sort of, but I’m still not clear on the atmospheric conditions that brought about our soggy planet (much more soggy during the Mesozoic though). In any case, I’ve recently read that bonafide researchers on this topic have also been mystified about the sheer volume of water on Earth.
Enter a new (to me) hypothesis, published in the Journal of Geophysical Research: Planets a little over a year ago. It argues – and other astrophysicists appear to be impressed by the reasoning and the detailed analysis in the paper – that the water came not only from asteroids but also from the solar nebula.
Solar nebula? Never heard of it, but apparently the concept has a long history. The so-called nebular hypothesis for the formation of our solar system was first proposed by Emanuel Swedenborg in the 1730s, and further elaborated by such luminaries as Immanuel Kant and Pierre-Simon Laplace later in the 18th century. Surprisingly for such an early contention, it has stood the test of time and survives today, though the details are still argued, and there are a few competing hypotheses. In any case, without going into too much detail, a nebula of dust and gas began to form around 4.6 billion years ago, and collapsed in on itself due to gravitational forces, spinning around a newly-formed sun. Out of this material, protoplanets gradually formed.
Water in the Earth’s oceans has approximately the same D/H (deuterium to hydrogen) ratio as that of the above-mentioned asteroidal carbonaceous chondrites, so it has always seemed a safe bet that most if not all water came from those asteroids. Yet the sheer volume of water was still a problem. Jun Wu, the lead author of the recent paper, had this to say about the theoretical situation:
The solar nebula has been given the least attention among existing theories, although it was the predominant reservoir of hydrogen in our early solar system.
What has apparently added credence to the new hypothesis is that samples of hydrogen near the core of the Earth have significantly less deuterium and may fit better with the ratio of hydrogen in the solar nebula. Also the isotopic signatures of the noble gases helium and neon found in the Earth’s mantle fit the signatures of these gases from the time of the solar nebula. The explanation of how the lighter hydrogen found itself drawn to the Earth’s centre, in a process called isotropic fractionation, is provided in the paper, apparently. It’s a very interesting story, if true, and it may have implications for liquid water on habitable-zone exoplanets. That’s to say, there’s no reason for it not to be quite common. Here, to finish, are a couple of thought-provoking comments from members of the research team.
… there’s another way to think about sources of water in the solar system’s formative days. Because water is hydrogen plus oxygen, and oxygen is abundant, any source of hydrogen could have served as the origin of Earth’s water.
Our results suggest that forming water is likely inevitable on sufficiently large rocky planets in extrasolar systems.
References
How did Earth get its water?
https://www.britannica.com/science/solar-nebula
a little about the chemistry of water and its presence on Earth
getting mildly excited about water
I’ve generally thought that the extraordinary volume of water on our planet’s surface was a problem, scientifically speaking, but I’m probably wrong. I used to think that the idea that water came to Earth in meteor showers (haha) couldn’t be right, because the days of Earth’s heavy bombardment came early in the planet’s history when everything was molten hot and the water or ice from meteors would’ve just boiled away. But what would I know? And why would meteors, or planetesimals, be so full of water?
As the astronomers are constantly telling me, water in solid, liquid and gaseous form is commonplace in our solar system, our galaxy, our universe. In the habitable zones of our universe it can exist in all three forms close together, and that’s what presumably makes those regions habitable. On Earth we have a hydrological cycle – evaporation and transpiration, condensation, and precipitation – involving the three forms of this precious stuff, more or less. Recently, some fuss was made about water found in the atmosphere of a not-so-distant exoplanet, and the female interviewer was seemingly excited about – hey, water, and maybe life!!! – but the scientist was much more impressed by the detection abilities we’ve developed for working out the chemical signature coming from distant bodies (this one was about 100 light years away – our galaxy is many thousands of light years across). Water in the atmosphere and even on the surface of these bodies is unsurprising, apparently.
When you (I mean I) consider that hydrogen is the simplest and most abundant element in the universe, and oxygen is also a relatively simple and abundant molecule, we shouldn’t be surprised that water is commonplace. As the above-mentioned scientist pointed out, water is found in the interstellar medium between star systems, amongst gas clouds, and within our solar system, especially in the material of the Kuiper Belt and in the ‘ice giants’, Neptune and Uranus. More excitingly for the possibilities of life, liquid, flowing water has been found on Mars – albeit highly salinated and mineral-rich. There’s still a possibility, though, that less ‘contaminated’ water may be found nearer the Martian poles. It’s also seen as a sign that Mars is drying up, water-wise, that it was once a much more watery world, and for a long time. Could it have seeded life on Earth?
Water worlds are being found elsewhere in the solar system too. The Cassini spacecraft has made major discoveries about Enceladus, a tiny, very bright moon of Saturn. Jets of water vapour, ice and surprisingly large quantities of organic chemicals burst out from below the moon’s icy crust at tremendous velocity. Some of the material is added to Saturn’s particulate ring system. The E ring’s particles, where the Enceladus material ends up, have been examined by Cassini, and in short, the examination suggests that there are hydrothermal vents beneath the icy shell of the moon, similar to those underneath the Pacific Ocean. Cassini’s analysis has also strongly indicated an ocean with a depth of around 10 kilometres underneath the thick ice (30-40 kms) at the southern polar region.
There are other promising watery discoveries too, and a relatively new theory about water on Earth, which I’ll leave for another post.
References
NASA discovers a water world in our solar system (mashable video)
https://imagine.gsfc.nasa.gov/features/cosmic/milkyway_info.html
https://solarsystem.nasa.gov/missions/cassini/science/enceladus/
How did Earth get its water?
how to define a planet: the problematic case of Pluto
A while back I listened to a podcast from Point of Inquiry, in which two planetary scientists, Alan Stern and David Grinspoon, involved in NASA’s New Horizons mission to Pluto, were separately interviewed, and were inevitably asked about Pluto’s demotion from planet status. Having not followed this issue, I was surprised at the response. So it’s time to take a closer look.
Of course I should be writing ecstatically about the New Horizons mission, not to mention those of Juno, Cassini, Mars’ Curiosity and so forth, and hopefully that will come, but the controversy about Pluto immediately struck me, as I thought, in my naïveté, that its demotion was a consensual thing amongst astronomers, with only the ignoroscenti (my neologism) left to mourn the fact (not that I mourned it particularly – Pluto still existed after all, and it didn’t care a jot what we thought of it).
Pluto, discovered by Clyde Tombaugh in 1930, was accepted as the ninth and final planet in our solar system for decades until the nineties, when another Kuiper belt object was discovered (besides Charon, Pluto’s large moon), and the Kuiper belt itself became a thing, in fact a massive thing, far bigger than the ‘familiar’ asteroid belt between Mars and Jupiter. We now know of more than 1000 kuiper belt objects, with at least 100,000 believed to exist. The Kuiper belt is widely spread out from the orbit of Neptune, and though Pluto is its largest and brightest object, it’s not the most massive. Presumably it’s for this reason that Pluto was demoted – what with the scattered disc and the Oort cloud there seemed to suddenly be a host of objects that could be included as planets, so it was thought better to exclude Pluto, or to demote it to dwarf planet status, presumably along with other assorted Kuiper belt objects (KBOs), rocks and iceballs that were worthy of the designation. That seemed okay to my thoughtless mind, but here’s what Alan Stern had to say on the subject:
Well, you know, we don’t really honour that classification in planetary science, that was really done by a group of different astronomers who don’t know much about planets. Let me give you a technical term, we call it BS. You know what BS stands for don’t you? Bad Science. Now you wouldn’t ask a podiatrist, a foot doctor, to help you if you had a cardiovascular problem with your heart, that’d be the wrong expertise, though they’re both doctors you’d be going for a cardiologist. And if you had a real estate problem you probably wouldn’t go to a divorce attorney, even though they’re both attorneys. In the space field we have many professions, we have engineering professions, we have many different scientific specialties, etc. Astronomers really don’t know much about planets any more than I’m an expert in black holes in faraway galaxies. They had a little meeting in 2006, they were worried that school children would have to memorise the names of too many planets, so they wrote a definition that limited the number of planets to eight. Now, right after that, Ira Flatow called me up on Science Friday and said, would you debate Mike Brown, who was one of the proponents of ‘let’s limit the planets to eight’, and I said, sure, and we got on the phone and it’s Science Friday live, and Mike Brown makes his case and says, ‘look we just can’t have 50 planets, it’s too many to remember.’ Now, I found that anti-scientific, it seems like engineering the definition, versus letting it inform you, but Ira said, Alan what’d you think, ‘can’t have 50 planets’, what d’you say back to MIke? I said, ‘well if you can’t have 50 planets then we’re probably going to have to go back to eight states, I guess’. And he was speechless…
I love that story – though no doubt Mike Brown would’ve told a different one. So let’s turn Stern’s objection into an inquiry. Was it scientifically correct/accurate/fair to reclassify Pluto as a dwarf/minor planet?
Happily I just happened to listen to a podcast of the Skeptics’ Guide a few days later, which has led me to a more detailed piece on Steven Novella’s Neurologica blog on the Pluto controversy. Apparently, in the above-mentioned 2006 meeting they decided that to be classified as a planet, a body in our solar system should meet 3 criteria:
- it has to orbit the sun
- it has to be spheroid (i.e. have the mass to be so, due to its gravity),
- it must have cleared its orbit of other objects.
Now this third criteria immediately seems the dodgiest, as it sounds like it’s designed to eliminate any KBOs. And how do we know an orbit is cleared? After all, one day, a comet or asteroid may strike us, because our orbits have coincided this time around. And why is that third criterion even important?
Novella cites a recent paper by planetary scientist Phillip Metzger who argues that the third criterion is invalid and that nothing about a body’s orbit should be in the definition since orbits can alter due to external influences. Only characteristics intrinsic to the body should be included in the definition. This would essentially leave one criterion standing – that of sphericity. And even then, how sphere-like does a planet have to be? Another ‘problem’ with Metzger’s definition is that it would include moons, such as our own, and many others. Novella has his own classifying suggestion, which sounds promising to me:
We keep criteria “a” and “b” and drop “c”. However, we add that the object must not be in a subservient orbit around a larger object. What does that mean? If two objects, like the Earth and Moon, are in orbit around each other, and the center of gravity (barycenter) lies beneath the surface of one of the bodies, then the smaller object will be said to orbit the larger object, and is a moon. Therefore Europa, which is large enough by itself to be a planet, would instead be considered a moon because it orbits Jupiter.
I need to further explain the term ‘barycentre’, for my own sake. Think of two bodies in gravitational relationship to each other. Inevitably, one of them will be more massive, and will exert a greater gravitational force. An obvious case is the Earth and the Moon. Between the two there is a point, the ‘centre of gravity’, or barycentre, around which the two bodies revolve, but because the Earth is a lot more massive that the Moon and they’re relatively close to each other, that barycentre is actually close enough to the Earth’s centre to be within the mass of the Earth, with the result that only the moon revolves. The Earth, though, is very much affected by the Moon’s gravitational field, which causes a slight wobble as well as tidal effects on the Earth’s surface.
Interestingly, Novella’s reclassification would include Charon, Pluto’s ‘moon’, as a planet (as well as Pluto of course) because its size relative to Pluto puts the barycentre at a point between the two bodies, rather than within Pluto. So Pluto-Charon would be reclassified as a binary-planet system. It would also promote Ceres, in the asteroid belt, and Eris and Makemake, two recently discovered Kuiper belt objects, to planetary status. That takes the current eight up to thirteen, with others yet to be discovered.
It’s unlikely of course that the astronomical overlords who reclassified Pluto would be swayed by any mere outsider’s view, however well-reasoned, but this examination of the issue is a reminder of just how dubious the reasoning of ‘experts’ can be, and how important it is to question that reasoning. Size apparently does matter to these guys, but this new category of ‘dwarf’ or ‘minor’ planet seems inherently unstable, and will probably become even more so as the number of discovered exoplanets increases. Will it be mass or volume that’s the decider, and what will be the mass or volume that decides? And does it really matter? It’s only nomenclature after all. And yet… The difference between an asteroid and a comet is important, is it not? And so is the difference between a planet and an asteroid. And so is the difference between a moon and a planet. And so… is it not?
Proxima b
Quote of the day/week/month/post:
Better to have questions you can’t answer than answers you can’t question – Max Tegmark (and many others)
Jacinta: So while astrophysicists argue over the likelihood of life elsewhere in our tiny but massive universe, some are focusing on our nearest star neighbour. Some wobbling of the red dwarf known as Proxima Centauri has revealed, upon lengthy observation, that it has a closely orbiting planet, which considering the relative coolness of the star – way too dim to be seen with the naked eye – and the proximity of its satellite, is very much in the habitable zone. While it’s too early to say so much for the naysayers, the discovery of a planet in the Goldilocks zone of our nearest star in a galaxy of billions of possibilities must surely raise hopes and expectations of life abundant.
Canto: This closest possible exoplanet was only discovered in August this year, so we’re desperate to find out more about it. Being in the habzone is one thing, habitability is another. Obvious questions we have no current way of answering are: does it have an atmosphere? Any possibility of water? Is it tidally locked? And of course we’d love to know if we could launch some sort of robotic mission to our nearest star neighbour. Meanwhile is there any other way of gleaning more info from this tantalising object?
Jacinta: It’s not likely to be habitable though. Solar winds are estimated to be some 2000 times those experienced on Earth, though we can’t be too sure. Researchers are trying to work out the size of the planet…
Canto: How do they know about those solar winds?
Jacinta: Oooh, that’s a horribly good question. It’s due to the closeness of the orbit, where you would expect the solar winds to be much stronger, as they are in our solar system. It’s believed that Mercury’s magnetic field, which should be stronger than it’s been measured to be because of its heavy metallic core, is dampened massively by our solar wind. So basically they would’ve inferred Proxima Centauri’s wind by our own. As to how they came up with the figure of 2000 times that experienced on Earth, I’ve no idea, but strong solar winds make it hard to maintain an atmosphere, which is vital for life. You’ve also talked about tidal locking, which is a feature of close orbits, such as the Moon’s orbit of the Earth. So you’ll have a permanently hot day side and a permanently cool night side, and this can be problematic for the creation of an atmosphere, according to modelling.
Canto: Now, all of this sounds very negative, but basing exo-planetary activity on what’s been the case, as far as we can work it out, in our solar system, has been really problematic hasn’t it?
Jacinta: Definitely, that’s why we need to go beyond modelling, if we can, and collect some real data. So we’re looking to the James Webb Space Telescope (JWST), the very exciting successor to Hubble to be launched around November 2018, to garner more info, which it’ll be perfectly equipped to do.
Canto: If by some near-miraculous combination of circs there is an atmosphere on Proxima b, or a reasonable quantity of liquid water, that would help distribute the heat around the planet. With no atmosphere, the difference between day side and night side would be stark.
Jacinta: Exactly, and that’s what the JWST should be able to detect, as the best way to detect the atmosphere is to measure the planet’s infrared heat signature. If the JWST finds a decisive and fixed difference between the planet’s day and night sides, it’s a safe bet that no atmosphere is present. The JWST will be equipped to measure this IR signature on both sides of the planet, and if it doesn’t find that stark difference, that’ll be when we can start speculating about an atmosphere and its constituents.
Canto: Though of course they’ve already started with the speculation. But really, whatever they find – and I don’t expect that everything will line up for life – the fact that we’ve found an exoplanet well worth investigating on the nearest star outside our solar system, with billions of stars yet to be homed in on, one by one – doesn’t that say something to those who argue for the Fermi paradox – where are they? Okay, Fermi and Hart were talking about intelligent life, and that may well be orders of magnitude more difficult to develop than life itself, but I’m sure that Fermi would be unsettled in his skepticism, if he was alive today, by the vast numbers of exoplanets, in other words possibilities for life, we’re discovering now, with so many to come in the near future.
Jacinta: Yes, bliss in this time it is to be alive, but to be young, that would be very heaven!
Cosmos issue 71, pp9-10
http://www.gizmodo.com.au/2016/08/how-well-get-our-first-big-clue-about-life-on-proxima-b/
en.wikipedia.org/wiki/Proxima_Centauri_b