As if paying tribute, exoplanets orbiting white dwarfs appear to be throwing their exomoons into hot atmospheres of these stellar husks.
This fascinating conclusion comes from a recent study into white dwarf stars that appear to have atmospheres that are “polluted” with rocky debris.
A white dwarf forms after a sun-like star runs out of hydrogen fuel and starts to burn heavier and heavier elements in its core. When this happens, the star bloats into a red giant, beginning the end of its main sequence life. After the red giant phase, and the star’s outer layers have been violently ripped away by powerful stellar winds, a small bright mass of degenerate matter (the white dwarf) and a wispy planetary nebula are left behind.
But what of the planetary system that used to orbit the star? Well, assuming they weren’t so close to the dying star that they were completely incinerated, any exoplanets remaining in orbit around a white dwarf have an uncertain future. Models predict that dynamical chaos will ensue and gravitational instabilities will be the norm. Exoplanets will shift in their orbits, some might even be flung clear of the star system all together. One thing is for sure, however, the tidal shear created by the compact white dwarf will be extreme, and should anything stray too close, it will be ripped to shreds. Asteroids will be pulverized, comets will fall and even planets will crumble.
Now, in a science update based on research published late last year in the journal Monthly Notices of the Royal Astronomical Society, astronomers of the Harvard-Smithsonian Center for Astrophysics (CfA) have completed a series of simulations of white dwarf systems in an attempt to better understand where the “pollution” in these tiny stars’ atmospheres comes from.
To explain the quantities observed, the researchers think that not only is it debris from asteroids and comets, but the gravitational instabilities that throw the system into chaos are booting any moons — so-called exomoons — out of their orbits around exoplanets, causing them to careen into the white dwarfs.
The simulations also suggest that as the moons meander around the inner star system and fall toward the star, their gravities scramble to orbits of more asteroids and comets, boosting the around of material falling into the star’s atmosphere.
So there you have it, planets, should your star turn into a white dwarf (as our sun will in a few billion years), keep your moons close — your new stellar overlord will be asking for a sacrifice in no time.
On Monday, I appeared on RT America’s live news broadcast to talk exoplanets — particularly the three small (possibly rocky) worlds that orbit the stars Kepler-62 and Kepler-69. It was a lot of fun discussing ‘Goldilocks Zones’ and the possibilities of extraterrestrials. Enjoy!
The first exoplanet was discovered orbiting a Main Sequence star in 1995, and the rate of exoplanet detections has been accelerating ever since.
It is worth noting that hundreds more candidate exoplanet detections have been made, many of which have been spotted by NASA’s Kepler space telescope. Kepler is staring at the same patch of sky, waiting for alien worlds to cross the line of sight between their parent star and Earth, registering a slight dip in starlight brightness. The 1,235 candidates will be confirmed (or denied) as Kepler awaits future transits.
Detecting the slight dimming of starlight isn’t the only tool exoplanet hunters have to spot these alien worlds. The “radial velocity” method — as employed by systems such as the ESO’s HARPS — can detect the slight “wobble” of stars as orbiting worlds gravitationally “tug” on their parent stars. Both methods have their advantages and both are notching up an impressive exoplanet count. “Microlensing” has also been employed to spot a handful of exoplanets, as has direct imaging.
Exoplanetary studies are amongst the most exciting astronomical projects out there. Not only are we realizing there is a veritable zoo of worlds — some Earth-sized, others many times the mass of Jupiter — we are also pondering the most profound question: could extraterrestrial life inhabit these worlds?
For now, we have no clue, but life as we know it has a habit of springing up where we least expect it, it’s only a matter of time before we start to have some clue as to the existence of life as we don’t know it.
Imagine the scene: I’m having a romantic walk on a clear night with my wife along the beach. We see a brief flash of light and Deb says, “Hey, a meteor!” I then proceed to tell her that most meteors are actually no bigger than a grain of sand and they originate from comets, even though she already knew that. Feeling quite chuffed with myself that I was able to describe a nugget of atmospheric dynamics in 2 minutes, Deb then points up again and says, “There’s Orion. What constellation is that one?”
“Um. I have no idea,” I reply, feeling less smug. “I know how those things work, but I don’t know what they look like.”
I don’t own a telescope (yet) and I only took one course in university on practical astronomy, everything else was astrophysics. So the sad thing is that I know how stars work — from the nuclear fusion in their core to coronal dynamics (the latter of which I did my PhD in) — but if anyone asked me to point out a constellation or the location of a star… I wouldn’t have a clue.
Sure, there are the old favorites, like Orion, the Big Dipper (or Plough) and bright Polaris, but my expertise in night sky viewing is pretty limited. Although I’d usually refer any astronomy-related questions to BBC astronomy presenter (and Discovery News writer) Mark Thompson, I’d love to learn more. So, firstly, I needed a star chart.
Luckily, a few weeks ago, I received a random email from Erik Anderson from Ashland Astronomy Studio asking whether I’d like a copy of his company’s new star map poster. Being eager to boost my pitiful knowledge of the constellations, I jumped at the chance. Soon after, my poster arrived through the post.
Now this is where things got really cool. Although Erik had titled his email to me “Star Map with Exoplanet Hosts,” I’d forgotten about the “exoplanet” part. On the clear, yet detailed Ashland star map, all the major constellations and stars are plotted, along with the time of the year (in the Northern Hemisphere) they can be seen. But also, there’s a symbol representing the hundreds of stars that are known to have exoplanetary systems orbiting.
Over the last couple of weeks, I’ve been referring to my newly-framed star map, and can now confidently point into the sky, not only identifying the constellations but also some stars that possess exoplanets. Only last night, I pointed up in the general vicinity of the star 61 Virginis (near the blue giant Spica) and said, “That star has 3 worlds orbiting it.”
I’m not sure if Deb was overly impressed with my exoplanet knowledge, but I was happy to be smug again.
Although it’s only a very small part of an astronomer’s tool kit, a star map is essential. Although you can get apps for your iPhone, you can’t beat a poster that isn’t only functional, but also looks very attractive on your office wall.
In 2009, I wrote about a fascinating idea: in the hunt for “Earth-like” exoplanets, perhaps we could detect the radio emissions from a distant world possessing a magnetosphere. This basically builds on the premise that planets in the solar system, including Earth, generate electromagnetic waves as space plasma interacts with their magnetospheres. In short, with the right equipment, could we “hear” the aurorae on extra-solar planets?
In the research I reviewed, the US Naval Research Laboratory scientist concluded that he believed it was possible, but the radio telescopes we have in operation aren’t sensitive enough to detect the crackle of distant aurorae. According to a new study presented at the RAS National Astronomy Meeting in Llandudno, Wales, on Monday, this feat may soon become a reality, not for “Earth-like” worlds but for “Jupiter-like” worlds.
“This is the first study to predict the radio emissions by exoplanetary systems similar to those we find at Jupiter or Saturn,” said Jonathan Nichols of the University of Leicester. “At both planets, we see radio waves associated with auroras generated by interactions with ionised gas escaping from the volcanic moons, Io and Enceladus. Our study shows that we could detect emissions from radio auroras from Jupiter-like systems orbiting at distances as far out as Pluto.”
Rather than looking for the magnetospheres of Earth-like worlds — thereby finding exoplanets that have a protective magnetosphere that could nurture alien life — Nichols is focusing on larger, Jupiter-like worlds that orbit their host stars from a distance. This is basically another tool in the exoplanet-hunters’ toolbox.
Over 500 exoplanets have been confirmed to exist around other stars, and another 1,200 plus exoplanetary candidates have been cataloged by the Kepler Space Telescope. The majority of the confirmed exoplanets were spotted using the “transit method” (when the exoplanet passes in front of its host star, thereby dimming its light for astronomers to detect) and the “wobble method” (when the exoplanet gravitationally tugs on its parent star, creating a very slight shift in the star’s position for astronomers to detect), but only exoplanets with short orbital periods have been spotted so far.
The more distant the exoplanet from its host star, the longer its orbital period. To get a positive detection, it’s easy to spot an exoplanet with an orbital period of days, weeks, months, or a couple of years, but what of the exoplanets with orbits similar to Jupiter (12 years), Saturn (30 years) or even Pluto (248 years!)? If we are looking for exoplanets with extreme orbits like Pluto’s, it would be several generations-worth of observations before we’d even get a hint that a world lives there.
“Jupiter and Saturn take 12 and 30 years respectively to orbit the Sun, so you would have to be incredibly lucky or look for a very long time to spot them by a transit or a wobble,” said Nichols.
By assessing how the radio emissions for a Jupiter-like exoplanet respond to its rotation rate, the quantity of material falling into the gas giant from an orbiting moon (akin Enceladus’ plumes of water ice and dust being channeled onto the gas giant) and the exoplanet’s orbital distance, Nichols has been able to identify the characteristics of a possible target star. The hypothetical, “aurora-active” exoplanet would be located between 1 to 50 AU from an ultraviolet-bright star and it would need to have a fast spin for the resulting magnetospheric activity to be detectable at a distance of 150 light-years from Earth.
As we’re talking about exoplanets, magnetospheres and listening for radio signals, let’s throw in some alien-hunting for good measure: “In our Solar System, we have a stable system with outer gas giants and inner terrestrial planets, like Earth, where life has been able to evolve. Being able to detect Jupiter-like planets may help us find planetary systems like our own, with other planets that are capable of supporting life,” Nichols added.
Although Nichols isn’t talking about directly detecting habitable alien worlds (just that the detection of Jupiter-like exoplanets could reveal Solar System-like star systems), I think back to the 2009 research that discusses the direct detection of habitable worlds using this method: Aliens, if you’re out there, you can be as quiet as you like (to avoid predators), but the screaming radio emissions from your habitable planet’s magnetosphere will give away your location…
For this special little planet, today has been a very big day.
Although we’ve speculated that planets the size of Earth must exist elsewhere in the cosmos, it wasn’t until one of the co-investigators working with the Kepler Space Telescope said he had statistical evidence that worlds of the approximate size of Earth appear to dominate our Milky Way.
We now know Earth isn’t unique.
Alas, this historic news didn’t come without controversy. It was unofficially broken at a TED conference in Oxford earlier this month and only after a recording of a presentation given by Dimitar Sasselov was posted online did the news get out. What’s more, the announcement only became clear when Sasselov referred to a presentation slide depicting a bar chart with the different sizes of exoplanets discovered by Kepler:
This slide shows the number of exoplanets discovered up until this month, binned by size. We have Jupiter-like exoplanets, Saturn-like exoplanets and Neptune-like exoplanets, all compared with Earth’s radius.
The heart-stopping moment comes when looking at the bar that represents Earth-like exoplanets (i.e. worlds with a radius of below 2 Earth radii, or “<2 Re"). According to Sasselov, Kepler has detected a lot of Earth-like worlds, so many in fact that they dominate the picture. From what we have here, it would appear that around 140 exoplanets are considered to be like Earth.
“The statistical result is loud and clear,” said Sasselov. “And the statistical result is that planets like our own Earth are out there. Our Milky Way galaxy is rich in these kinds of planets.”
But why the controversy? Isn’t this good news?
It would appear that the Kepler co-investigator chose not to wait until the official press release from NASA. He publicized these groundbreaking results in the U.K. at an event where you had to buy tickets to attend. This isn’t usually the stage you’d expect this kind of discovery to be announced — a move that will undoubtedly upset many.
“What is really annoying is that the Kepler folks were complaining about releasing information since they wanted more time to analyze it before making any announcements,” Keith Cowing, of NASAWatch.com, wrote in a SpaceRef article today. “And then the project’s Co-I goes off and spills the beans before an exclusive audience – offshore. We only find out about it when the video gets quietly posted weeks later.”
This sentiment is understandable. Only last month there was some frustration vented at the Kepler team for holding back data on 400 exoplanet candidates. While this might be standard practice — the discovering team should be allowed some time to publish work on any discoveries they have uncovered — telling the world’s scientists they will have to wait until February 2011 before they can get their hands on this invaluable data was a bridge too far.
In light of this, for a Kepler scientist to then jump the gun and disclose a groundbreaking discovery at an international conference without the backing of an official NASA release seems a little hypocritical.
But there is another argument to put out there: Why should anyone sit on such a profound discovery? Perhaps NASA and the Kepler team should have issued an earlier press release announcing to the world that 140 candidate Earth-like worlds have been detected and that further work will need to be done to confirm.
Ultimately, this controversy is just background noise when compared to what we have learned today. Official confirmation or not, Dimitar Sasselov’s message is clear. Although these detections need to be confirmed (hence why these worlds are referred to as “candidates”), it would appear there is an overwhelming preponderance of exoplanets measuring 2 Earth radii or less.
For me, that fact alone is astonishing — the first scientific evidence that worlds of Earth dimensions are not rare.
The first results from NASA’s Kepler exoplanet hunter are in and a perplexing early result has been announced. Yes, the space telescope is working fine, and no, it hasn’t spotted an alien homeworld (yet), but the Kepler team have uncovered something pretty cool.
Kepler may have discovered a new class of celestial object (possibly).
But before we start scratching our heads in confusion or popping the champagne corks in celebration, let’s try to work out what Kepler has observed.
Kepler is currently monitoring 100,000 stars in an effort to seek out extra-solar planets (or “exoplanets”) orbiting these stars. Although Kepler was only launched in March 2009 and early doubts about the observatory’s capabilities caused some low-level concern, Kepler appears to be functioning well and mission controllers are already reporting early results.
In sifting through the Kepler data taken so far, postdoctoral student Jason Rowe found a very curious light signature. When an object passed behind its central star, the light from the system dropped significantly. This means the object — called KOI 74b — must be glowing fiercely with its own light that was blocked out when the object was eclipsed.
Hold up, the light dimmed when the exoplanet passed behind its parent star? Something’s not right here. Kepler detects exoplanets when the worlds pass in front of their parent stars, thereby dimming the starlight, not vice versa!
Actually, this is exactly what’s happened. The “exoplanets” orbiting two otherwise ordinary stars appear to be brighter — and hotter — than their host stars. It’s as if the roles of the stars and the exoplanets have been reversed; the stars are dimming the exoplanetary light as the exoplanet passes behind the star.
Needless to say, there is currently no stellar model that predicts this kind of behavior from extra-solar planetary systems.
This means the object — called KOI 74b — must be glowing fiercely with its own light that was blocked out when the object was eclipsed […] It is seething at 70,000 degrees Fahrenheit while the parent star is 17,000 degrees Fahrenheit. The strange object can’t be a star because the transit data show that it is no bigger than Jupiter. —Ray Villard, Discovery News.
One theory is that KOI 74b (and the other strange object, KOI 81b) could be a white dwarf star that migrated close to its stellar partner. Through binary interactions, the white dwarf was stripped of some of its mass, causing it to puff up and appear like a gas giant exoplanet. That would certainly go to some way of explaining why these two “exoplanets” are so hot.
Of course, the other option is that Kepler has made a groundbreaking discovery and identified a whole new class of celestial object… but I suspect there are other, more mundane reasons for these observations.
I suppose we’ll just have to wait and see until followup observations are made…
On reading an article in The Daily Galaxy today, I was interested by what the author had to say. In a nutshell, the article pointed out that it is a big mistake to believe we are the only intelligent life in the Milky Way.
Why is that?
The only reason given was that there are billions of stars, it is therefore foolish to think we are the only example of an advanced species. Unfortunately, there is no evidence to suggest that we aren’t the only intelligent life form in our galaxy. Just because there are hundreds of billions of stars possibly with billions of habitable planets does not constitute evidence that we’re not alone. That’s what science is all about, formulating a theory and then gathering the evidence. Simply saying, “There’s lots of stars, therefore there must be an intelligent species out there,” doesn’t cut it.
Dr Frank Drake toiled with this idea to eventually arrive at the famous Drake Equation, a concept I have never felt at ease with:
How can you arrive at the conclusion that we are not the only intelligent life in the galaxy simply because there are a lot of stars?
It is true that the Milky Way contains billions of stars, of which a high percentage probably have exoplanets not dissimilar to Earth orbiting them. There’s every chance that a smaller percentage of those Earth-like terrestrial exoplanets have some kind of basic life form slivering around (or indeed swimming, flying, walking or ‘talking’). Also, there’s the chance that some of these exoplanets have nurtured something that we’d consider to be ‘intelligent.’
Now this is where things start to get a bit tricky.
There are massive international efforts under way to find any kind of extraterrestrial life. We’re toasting soil samples on Mars in the hope of finding the biological signature, and we’re using full-blown antennae scouring the skies for any organized signal from an intelligent alien species. However, whether we are looking for microbial life in the Solar System or something a little more sophisticated beyond, our search for extraterrestrial life is based on only one model: Earth.
It’s all very well saying that we should be looking for other possible forms of life, but if we have no experience of it, how do we know what to look for?
It’s a similar question to, “What is beyond a black hole’s event horizon?” We have no idea, because we cannot experience it, the physics of our Universe simply do not apply beyond an event horizon.
There are a lot of ideas, theories and conjecture but at the end of the day, we have to assume ET will have some trait we are familiar with.
When looking for intelligent extraterrestrials we make the assumption that these civilizations have progressed in a similar way to us, eventually transmitting radio signals (perhaps even laser beacons) to communicate on their home world, between planets with their own kind, or even reaching out into the cosmos, signalling their presence to other life forms capable of receiving interstellar signals.
We’ve been leaking radio signals into space for the last century and we are constantly communicating with our planetary probes. There’s every chance that if there’s an intelligent alien (with a radio receiver) within 100 light years, we may have already been detected. We are also being a bit more proactive these days, using programs such as Messaging Extraterrestrial Intelligence (METI) to make our presence known. (But what should we be saying?)
SETI, METI, SETA… SETT?
Unfortunately, apart from one isolated case, the Search for Extraterrestrial Intelligence (SETI) has drawn up blanks, we don’t think we’ve heard anything in the cosmos that’s originated from an alien.
The Milky Way is very old, in fact, the oldest star in our galaxy has been burning for 13.2 billion years (compare that with the age of the Universe at 13.74 billion years); you’d logically think that something resembling an intelligent civilization would have popped into existence in that time. If they did, surely we’d have detected them by now, wouldn’t we?
Actually, this spawns yet another debate: Have ancient interstellar alien civilizations come and gone? Was there a frenzy of intelligent life popping up all over the galaxy in the billions of years that our Sun was a proto-star surrounded by a proto-planetary disk? If old alien intelligence has since become extinct, our few thousand years as an evolving civilization is a mere spark in universal time scales. Could it be that we’ll have to wait until we can actually visit interstellar destinations first-hand to do the SETI equivalent of an archaeological dig, looking for alien artefacts? Perhaps SETI should be changed to the Search for Extraterrestrial Artefacts (SETA), where we’d have to look for evidence of alien civilizations past.
There’s another factor to consider. What if an advanced extraterrestrial civilization simply isn’t transmitting? If this is the case, perhaps we should consider a Search for Extraterrestrial Technology (SETT). In this case we could look for alien megastructures, searching for the stuff of science fiction. These structures could include examples of Dyson Spheres, huge alien-made hollow spheres containing a star; a means to harvest all the stellar energy for a vastly advanced civilization.
These are all options, and we shouldn’t close any possibility, no matter how extreme they may be.
There’s a reason why we haven’t received a signal via SETI, but we have no idea about what it could be. We really could be alone in the Milky Way. But then again, there’s a huge number of reasons why we might not be receiving a message from an intelligent species.
SETI may not be an interstellar switchboard, but the reasons for this are far from obvious. The theory that we are alone is just as valid as the theory that we are actually a part of a vast interstellar ecosystem. Until we have scientific evidence, we can’t say either way.
This is probably one of the biggest questions that hang over science fiction story lines: Will extraterrestrials have any resemblance to Life As We Know It™? To be honest, to toy with the thought of anything other than carbon-based life is pure conjecture, just because there might be some other form of life (such as silicon-based creatures), doesn’t mean there is (doesn’t mean there isn’t, either). So, here we are with the only form of life we know and understand, carbon-based life that was somehow spawned via a crazy mix of amino acids and some astronomical or terrestrial event that sparked the formation of prokaryotes (a.k.a. the simplest single-celled speck of life) some 4 billion years ago.
So we have an understanding of what formed life on Earth, perhaps if we look for the traces of evidence that evolved into Life As We Know It™ we can gauge whether extraterrestrial life has-formed/is-forming/will-form elsewhere in the observable Universe. From simulations of Earth evolution, scientists have predicted that 10 types of amino acids should form with the planet. These 10 amino acids are found inside the proteins of all living things on Earth. The same 10 amino acids have been found inside meteorites. Therefore, we already have a connection with the amino acids we find here on Earth and amino acids found in chunks of rock from elsewhere in the Solar System.
Now, a group of Canadian researchers have found that the same 10 amino acids are readily available elsewhere in the cosmos. Does this mean the components for life are common, not only on Earth, in the Solar System, but also in the Milky Way (and beyond)? It looks like it… Continue reading “Could Extraterrestrial Genes Be Like Ours?”
Is there a new way to hunt for habitable Earth-like exoplanets? According to a US Naval Research Laboratory researcher there is an obvious, yet ingenious, way of listening for these worlds. Like most Earth-like exoplanet searches, we are looking for characteristics of our own planet. So what do we need to survive on Earth? Obviously we need water and the correct mix of oxygen with other atmospheric gases, but what about the magnetic bubble we live in? The Earth’s magnetosphere protects us from the worst the Sun can throw at us, preventing the atmosphere from being eroded into space and deflecting life-hindering radiation.
Although we have yet to develop sensitive enough radio telescopes, it may be possible in the future to detect the radio waves generated as charged particles in stellar winds interact with Earth-like exoplanetary magnetospheres. If there’s a magnetosphere, there may be a protected atmosphere. If there’s an atmosphere, perhaps there’s life being nurtured below…