The Worlds of TRAPPIST-1

The internet is alight with people sharing the news of NASA's latest announcement. After teasing us with talk of a discovery "beyond the solar system," NASA announced the existence of a seven-planet star system located less than forty light years away. What's most exciting about the discovery is that most of the planets are considered potential habitats for life.

The star known as TRAPPIST-1 is, like many modern stellar discoveries, named after the device used to detect it, in this case, the TRAnsiting Planets and Planetesimals Small Telescope in Chile. You may notice that this doesn't quite spell out TRAPPIST, but the inventors are obviously Belgian beer fans and I can support that. Located 39 light years away in Aquarius, TRAPPIST-1 is described as an ultra-cool dwarf star, on the borderline of a red dwarf and a sub-stellar brown dwarf. Three planets were discovered there and announced back in 2015, and since then, the NASA Spitzer telescope and the Very Large Telescope at Paranal have detected four more. The extent of the system was announced last night (Feb 22nd).

In spite of being such a cool, dim star, TRAPPIST-1 may make an effective sun for life-bearing planets due to their extremely close orbits. All seven known planets orbit the star closer than Mercury orbits the Sun, and at least three of them are considered right within the system's habitable zone. This makes the planets astonishingly close together; the first and second planets are only slightly further apart than the Earth and the Moon. Finally, elaborate skies hanging with enormous sister planets can be considered a reality, not just science fiction. 

OK, this is Vulcan, but you get the idea

The planets are named TRAPPIST-1b through to -1h, and, unusually for discoveries of this type, are labelled in order of distance from their star. Each of them is within Earthlike mass and radius, with at least three of them estimated as being smaller than the Earth, and all are considered to be rocky, terrestrial-type planets. TRAPPIST-1b and -1c are the closest, with featureless spectra that indicates either a cloudless, water vapour dominated atmosphere, or a thicker, Venus-type atmosphere. They most likely lost the bulk of their surface water while their star was still cooling, and are less likely as abodes for life. TRAPPIST-1d is more likely habitable, although still closer than the calculated Goldilocks zone. TRAPPIST-1e, -1f and -1g are right within this zone, and are probably fairly cool in comparison to their inner brethren, far more likely to hold liquid water, Depending on the thickness of the atmosphere, they may be cooler than the Earth, or more comfortably terrestrial. TRAPPIST-1h is less well analysed so far, but is likely cold and less hospitable.

While the relative positions of planets to the star suggest potentially life-supporting temperatures, we shouldn't jump to conclusions. As always, Earthlike is a relative term. Red dwarf stars, let alone ultra-cool dwarfs, are debatable as life-supporting stars, due to the extreme proximity of their planets. The year on these planets will be very rapid, in the manner of a few days (-1b's year lasts only a day-and-a-half in Earth terms, with -1h at no more than 35 days, probably less). They are also likely to be tidally locked, with one side of each planet permanently facing the star. Both facts would lead to extreme weather conditions on the surface. Equally, radiation from the star, including X-rays and extreme energy ultraviolet radiation, would bombard the planets constantly at that proximity, depleting the atmospheres and making it harder for life to form.

Still, there is reason to hope. Even if the planets are lifeless now, they may not be always. Stars' longevity is inversely proportional to their size and temperature, and an ultra-cool dwarf like TRAPPIST-1 is likely to last a thousand times as long as the Sun, remaining stable for trillions of years. TRAPPIST-1 is estimated at only 500 million years old at present, but it could become a host for life for many thousands of millions of years in the future. 

Click the link here for NASA's announcement and an artist's impression of planet TRAPPIST-1d.

Latest news from interstellar space

So, it turns out there's a huge galaxy sitting right next to ours. Well, huge in terms of dwarf galaxies. Crater 2 has an effective half-light radius of 1100 pc, so that makes it at least 7000 light years across. It's the fourth largest satellite of the Milky Way (after the Magellanic Clouds and SagDEG), orbiting at relatively close distance (only 120 kpc), so it's quite astonishing that it's remained undetected until now. It is, however, remarkably dark - one of the dimmest galaxies ever seen. A vast collection of stars just swinging past ours for billions of years and we've only just noticed. It makes you wonder what else is out there; researchers are already planning ways to search for dark galaxies.

There's also the discovery of a new category of exoplanet: superearth-sized bodies which have been stripped of their atmospheres by close proximity to their parent star. If confirmed, these irradiated desert worlds would fill a gap in the variety of exoplanets already known, and give us a look at what might lie in wait for our own Earth in the distant future as the Sun expands.

Then there's the spectacular news that Stephen Hawking is teaming up with a wealthy Russian eccentric to begin research into a new space programme. It's summarised here at the Guardian, but the upshot is that we could be receiving data directly from Alpha Centauri in the next few decades. Hawking proposes that research and technological development could make the proposal, involving a swarm of tiny spacecraft accelerated to extreme velocities by laser beams, could be feasible in ten to fifteen years.

If successful, the starprobes could reach up to a fifth of lightspeed, allowing at least some of them to make the trip to Alpha Centauri in a mere twenty-five years. Once there, they will begin transmitting data back at lightspeed, meaning another four-and-a-half years before we receive updates. Sadly, Hawking will never get to see the fruits of the project, but a future generation of astrophysicists could be studying that data for years. If successful, the project could also revolutionise exploration of our own solar system - searching for the supposed ninth planet, for example. (Personally, I'll believe that one when there's some real evidence.)

The International Astronomical Union recently held a vote to determine the names of a list of planets and stars in distant systems. It would be impossible to assign a name to every star and planet in the Galaxy - there are just too many of them - so they generally just get an alphanumerical designation. However, a few have accrued names from popular usage, and now a select group have had names officially assigned by the IAU, according to popular vote.

The full list is at the link, but some of my favourites include Thestias, the new name of the only known planet orbiting Pollux (Beta Geminorum), named for the epithet of Leda, the mother of Castor and Pollux (the Gemini twins) in Greek myth. The Mu Arae system has five known planets, named for characters from the Don Qixote story: Quijote, Dulcinea, Rocinante and Sancho, plus the star itself has received the common name Cervantes, after the author.

Another star, formerly known only as PSR 1257+12, has been named Lich, and undead being from myth, and its planets have been named in kind: Draugr, Phobetor (i.e. Nightmare) and Poltergeist! The well known Epsilon Eridani is now also called Ran, and its sole known planet is Aegir, named for two Jotnar from Norse myth. And a particular favourite planet of mine, Fomalhaut b, is now known as Dagon, after the Semitic deity (made famous in the modern era by H.P. Lovecraft).

The 55 Cancri system has been named in honour of great astronomers, with the star itself now called Copernicus, and its planets named Galileo, Brahe, Lippershey, Janssen, and Harriot, while Iota Draconis b has been named for the great Hypatia. Wonderful stuff.

Warp Drive and Interstellar Travel

In the wake of the release of the full trailer for Christopher Nolan's upcoming movie Interstellar, 'Sploid' has produced a short article summarising the latest theoretical thinking on faster-than-light travel. Read it here (and watch the trailer there too).

The important things to remember are:

a) This is all very theoretical at the moment, and the questions about the energy requirements for warping space-time are still unanswered;

b) If the energy requirements are feasible, there will still be limitations on what we can produce. The "just punch it and you're there" comments in the subscript reveals a complete misunderstanding of the nature of the theoretical requirements. It will take vastly more energy to warp space sufficiently to travel at ten times the speed of light than at light speed itself, and orders of magnitude more to travel at higher speeds still. While interstellar travel through our local neighbourhood might be worth aiming for, travel across the galaxy is another major step beyond that. Intergalactic travel is likely to be simply unfeasible. 

c) However, relativistic problems are, indeed, irrelevant. According to all current understanding, baryonic matter and known forms of energy cannot exceed the speed of light. Indeed, nothing with an intrinsic rest mass could even reach it. However, an object within a warp field would not be travelling at superluminal speeds. It would be stationary relative to its own bubble of space, but the bubble itself would be shifting relative to its surroundings. By contracting space-time ahead of a ship and expanding it behind it, apparent superluminal speeds could be achieved without any relativistic effects or breaking the light barrier.

d) Even if the physicists demonstrate that this is possible for low mass experiments, we're a long, long way from developing actual warp drives for spacecraft.

e) The fact that we will very likely run out of drinkable water in the near future due to global temperatures rising and ever-growing populations is more of a major concern. I'm with the author on that, all the way. How flying to other star systems  is going to help with that, I don't know. No matter how earthlike a planet is, it isn't going to be anywhere near as suitable for us as even a depleted Earth.

Film looks good though.

Kepler continues

The big announcement in astronomy circles this week was the discovery of three more Earth-like planets by the Kepler spacecraft. There's a ton of coverage out there, but the New York Times is a good place to go for straightforward rundown of the finds.

Kepler-62e and 62f have 1.6 and 1.4 times the radius of the Earth, and lie comfortably within their stars theoretical habitable zone. Kepler-69c has a radius about 1.7 times that of the Earth. System K-62 lies around 1200 light years away, K-69 about 2700 ly.


Here's a nice artist's impression of all four Earth-like planets next to the Earth itself.

From left to right, we have the previously discovered K-22b, K-69c, K-62e, K-62f and Earth. The planets are shown to scale, but the look of the four new worlds is down to artistic licence.

Many of the articles turning up feature pretty rampant speculation as to how wonderfully hospitable for life these planets will be, with thick moist atmospheres and rolling oceans. However, these claims make a hell of a lot of assumptions as to the makeup of the planets and their systems. With only our own solar system to go on, we have little knowledge that is useful in predicting just how planets in other systems are likely to develop. Remember, also, that planetary scientists use 'Earth-like' in this context to mean any planet of size similar to Earth with a likely rocky makeup. This doesn't necessarily mean that the planet will have oceans and rolling green hills; Venus and Mars are Earth-like under these criteria.

A more illuminating look at the nature of our system compared to Kepler's discoveries can be seen here, at New York Times once again. It's a fascinating inforgraphic comparing the Kepler star systems.

Additionally, the good folk at Planet Hunters have had their own planetary discovery, provisionally named PH1b, accepted by the Kepler team and officially designated as Kepler-64b. The Planet Hunters website is open to all, allowing anyone to review the data and see if they can spot a previously unknown planet.

A quick trip round the block

A short video uploaded by the American Museum of Natural History, taking in the local stellar neighbourhood and stopping off at star system HR 8799.

Kepler-37

Another interesting star system discovered, this time by a crowd-funded astroseismological project. Kepler-37, 210 light years away in Lyra, has three observed planets, all on the smaller, rocky end of the scale. K-37b is the smallest exoplanet yet known, only about the size of the Moon! Surely we're going to have some kind of exo-dwarf-planet debate soon, if tiny ones like this are turning up? It's all on Wiki.

In a vaguely related note: I hereby suggest that any planetoid discovered that has its own moons should be named Gozer, and the moons Vinz Clortho and Zuul. Vigo and Ivo Shandor may be reserved for any further moons (after that we'd probably have to start raiding Real Ghostbusters characters).

Anyway, it's my birthday. I'm off to have fun.

Let's go meet the neighbours!

Alpha Centauri has a planet.

That's Alpha flippin' Centauri. The triple star system just over four light years away, the closest star system to our own. That's NEXT DOOR, in galactic terms. Hell, it's practically here. And to think I got enthused about Epsilon Eridani...

For anyone not in the know, Alpha Centauri is comprised of three stars: Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. A Cen A and B are both Sun-like stars, A being slightly larger and brighter, B being somewhat smaller and dimmer, and they form a binary pair. Proxima is a dim, old red dwarf, possibly captured by the binary pair, that orbits them at a distance of about a tenth of a light year and is currently, at 4.2 ly, the closest individual star to the Sun.

The new planet orbits A Cen B, and so its systematic name is Alpha Centauri Bb (but surely they'll come up with a proper name for such a nearby planet?) It was found after four years of studying the tiny Doppler shift in the starlight created by the planet's gravity, something extremely difficult to measure accurately. So, it's something of a milestone in planetary detection, even disregarding its proximity.

The planet is fairly unremarkable in itself. It's very low mass, approximately that of the Earth, but its also extremely close to its parent star, so is likely to have a surface temperature of over 1200 Kelvin. So there's no chance of friendly Alpha Centaurians living there. However, stars with one planet frequently turn out to have several more, so the hunt is on for more Centaurian planets; indeed, there's some suspicion that a planet  is orbiting Proxima, although this is unconfirmed.

SETI are getting ready to scan the direction of Alpha Centauri for possible radio signals, and presumably agencies will be looking at sending their own signals towards it. After all, it'll only take four years or so for a message to get there...

Lots more on the discovery here:

http://io9.com/5952357/scientists-discover-a-planet-in-alpha-centauri-the-star-system-nearest-earth
http://www.bbc.co.uk/news/science-environment-19959531
http://en.wikipedia.org/wiki/Alpha_Centauri_Bb

Planet Hunters

Just been reading the latest extrasolar planet news. The newly publicised planet PH1 is extremely cool for two reasons. Firstly, it was discovered by two volunteers at Planethunters.org, and secondly, it's got four suns!

PH1 is a Neptune-sized planet in a system around 5000 light years distant. The planet orbits a binary star - pretty fantastic in itself, seeing that such circumbinary planets were only confirmed to be possible a few years ago. Now, that binary pair, and beyond PH1 itself, orbit two more stars, in a second binary pair at a distance of roughly 1000 AU.

This is described as a 'hierarchical quadruple star system" featuring a planet orbiting an eclipsing binary. This is unexpected. When the two volunteer astronomers, K. Jek and R. Gagliano, reported their findings to Planethunters, the professionals got on the case and took a proper look at the system, confirming the analysis. They were understandably dubious of such a finding, since common consensus holds that such a system is impossible. The combined gravitational pulls of the four stars would be expected to tear the planet apart. Yet, there it is, happily orbiting one pair primarily and the next secondarily (much as the Moon orbits the Earth, and the Earth-Moon system orbits the Sun).

It's all a bit of a headscratcher. Plenty more information at io9 and arxiv.org

The nth Planet

The Planet Hab Lab have made available this very cool infographic displaying all 786 currently confirmed exoplanets. Hover the cursor over any planet and you'll get a readout telling you its relative size, plus its year of discovery and atmospheric type for certain examples (no distances, sadly). The handful of planets known that are Earth-sized and smaller are a little hard to pick out amongst all the super-jovians, but it's a nifty way to browse through the menagerie of worlds that have been discovered over the past few years.

Click on the image to go to the interactive infographic. Also, Douglas Adams fans should highlight the entire image for a fun extra.

More Earthlike exoplanets

A little update on the ongoing search for planets. NASA confirmed yesterday that the Kepler telescope has successfully located two planets of Earthlike size and mass. After the 'twin' planet of Kepler-22b getting all the fanfare, this latest discovery has slipped by with little fanfare, yet it's just as significant, since these are the first confirmed terrestrial planets of comparable size to our own.

The two planets have been located in star system Kepler-20, which has now been thoroughly investigated and has previously revealed three larger planets. With five planets, Kepler-20 is quite a busy system, although not the most populous known (HD 10180 and Kepler-11 both have a confirmed six planets, still behind our own system with its eight major planets). Kepler-20 is about 290 parsecs away (that's nearly 950 light years) in the constellation of Lyra, and is a reasonably close match to our own Sun.

So, these two new worlds, designated Kepler-20e and 20f, are the smallest ever found. Detecting planets this small isn't easy. There's a good article here on the discovery, which explains some of the long process that was required to confirm the discovery. There's also a nice little animation illustrating the planetary system.

The previously trumpeted planet Kepler-22b has a radius approximately 2.4 times that of Earth, while the previous record holder of smallest exoplanet was K-10b, the first confirmed terrestrial exoplanet with a radius of 1.4 Earths. It's clear to see that the Kepler project has been slowly getting closer to an Earth-sized planet. Now it has been rewarded with two. K-20f is the larger of the two, at 1.03 Earth radii, while its sibling K-20e is only at 0.87 of Earth's radius; roughly the size of Venus.

However, there's no use getting excited about alien life forms or comfortable planetary colony sites. All the planets found orbiting Kepler-20 do so much closer than Mercury does the Sun. K-20f is the outermost, and orbits in only twenty days. There is a slim chance it may retain an atmosphere of heavier chemicals - water vapour, perhaps - but K-20e, is in a six-day orbit, with an estimated surface temperature of 1040K, so there's no chance of it retaining any atmosphere.

It's a peculiar system altogether, really. Planet b is the innermost, followed by planets e, c, f and d - which means it's running big, little, big, little, big. The three larger planets are probably gaseous, and are somewhere in the super-Earth size band, smaller than Neptune - hot gas dwarfs. It's a far cry from our own system, with four terrestrial planets, two huge jovian gas giants and two smaller, colder gaseous planets, all much further from the Sun and from each other. It seems that the Solar System is by no means typical for the galaxy. It'll be very interesting to see what the next few planetary systems turn out to be like.

UPDATE: Only hours after I posted this, a further discovery was announced, detailing two planets found orbiting the star KOI 55 (aka KIC 05807616), a dying subdwarf. The two planets, KOI 55.01 and KOI 55.02 are even smaller than Kepler-20e, at 0.76 and 0.87 Earth radii respectively, and they have extraodinarily close orbits that last only a matter of hours. Betsy Green, one of the researchers on the project, has issued a statement saying that KOI 55 must have previously been a red giant star, having long since passed through this phase of its existence, and that the planets must have been drawn inside its mass during its giant period. Furthermore, to have survived this immersion in the star's outer layers, the planets must once have been gas giants, with their thick atmosphere's taking the brunt of the star's energy. The fluid layers would have been stripped away, leaving the dense metallic cores behind. Such planets, known as Chthonian planets, have been theorised before, but never definitively identified.

There's a detailed article on the findings here at the Daily Galaxy.

A new Earth?

The latest scientific story to grab the headlines is the discovery of planet Kepler-22b, an apparent 'twin' of the Earth. This is certainly a fascinating and important discovery, but the matter has been overstated.

Kepler-22b, located 600 light years away on the edge of Cygnus, is the most Earth-like planet so far discovered beyond our solar system. It is the first planet of a comparable size to our own to be confirmed to exist within its system's habitable zone. Smaller planets, closer to that of the Earth, have been detected, but so far all orbiting their primaries at close proximity that would likely make them too hot for life. Kepler-22 is a Class-G star, much like our own, but a little smaller and dimmer; the planet lies 15% closer to its star than we do to our Sun, putting it in a similar position heat- and radiation-wise.
So, the position is a good one, giving a potentially temperate environment for the planet. Yet the 'twin' aspect of Kepler-22b to Earth has been overstated by the stories. The planet has a radius about 2.5 times greater than the Earth's. That's a pretty good approximation of the Earth, in the scheme of things, but not quite what I'd call a twin. As a contrast, look at Venus. Venus is almost an exact match for Earth, size-wise, and is very similar in terms of structure and composition. It's also within the solar habitability zone, just about, so you would expect an environment very similar to that of the Earth. Yet Venus is a broiling hellhole, and any human being who set foot there would be immediately choked, crushed and boiled to death. Venus is a much better match for the Earth than Kepler-22b, but it's hardly a promising colony site.