About Those ‘Habitable’ Exoplanets (RT America Interview)

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!

Discovery News coverage of Kepler-62:

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Life: Not So Grim On The Galactic Rim?

M80 -- an old globular cluster in the Milky Way -- is full of metal-poor stars. Do they still have exoplanetary potential? (NASA)

M80 — an old globular cluster in the Milky Way — is full of metal-poor stars. Do they still have exoplanetary potential? (NASA)

The galaxy may be brimming with habitable small worlds and many older star systems could possess the conditions ripe for advanced alien civilizations to evolve. This prediction comes in the wake of new analysis of data from NASA’s Kepler space telescope and ground based observatories by a team of Danish and American astronomers.

Led by Lars Buchhave of the Niels Bohr Institute in Copenhagen, the team has revealed that stars containing low quantities of heavy elements — known as “metal poor” stars — are still capable of nurturing exoplanets with Earth-like qualities.

“I wanted to investigate whether planets only form around certain types of stars and whether there is a correlation between the size of the planets and the type of host star it is orbiting,” Buchhave said.

After analyzing the elemental composition of stars hosting 226 small exoplanets — some as small as the rocky planets in the Solar System — Buchhave’s team discovered that “unlike the gas giants, the occurrence of smaller planets is not strongly dependent on stars with a high content of heavy elements. Planets that are up to four times the size of Earth can form around very different stars — also stars that are poorer in heavy elements,” he concluded.

The Kepler mission, for example, is actively carrying out a search for exoplanets that pass in front of their host stars (events known as “transits”). With Kepler’s sensitive eye, it is capable of detecting exoplanets of similar size to Earth, or even as small as Mars.

Interestingly, as it surveys Sun-like stars, Kepler can detect tiny, rocky worlds that orbit within the “habitable zones” of their stars. It’s no huge leap of the imagination to think alien life may have evolved on some of these worlds.

But a problem facing astronomers hunting for bona fide “Earth-like” exoplanets is that many older stars have low quantities of heavier elements (such as the silicon and iron) that small rocky worlds need to become… well… rocky. But Buchhave’s discovery suggests that stars once considered infertile may in fact have a shot at birthing small exoplanets.

Jill Tarter, Chair of the SETI Institute, points out that this could be a boon for the search for intelligent extraterrestrials. “The idea that very old stars could also sport habitable planets is encouraging for our searches,” she said in a SETI press release on Wednesday.

Tarter also highlights the fact that life took a long time to evolve into an advanced technological state on Earth. Therefore, should there be small habitable rocky worlds orbiting ancient stars (as this research suggests), perhaps alien life far older and more technologically advanced than ourselves are out there.

Although this seems to make logical sense, it may not make biological sense. Metal-poor stars might have the ability to create small worlds, but just because there are likely many small worlds out there, it doesn’t mean life can be nurtured. But then again, regions of the Milky Way once considered to be devoid of exoplanets may now have a stab at providing a planetary habitat for extraterrestrial biology to gain a foothold. Whether or not these metal poor stars host the right ingredients for the building blocks of life probably won’t be known for some time.

In 2009, I wrote an article (see “Life Is Grim On The Galactic Rim“) that grabbed the attention of National Geographic writer Ken Croswell who quoted my Astroengine.com article in the December 2010 edition of the magazine. In the text, I discussed some research that investigated the strange lack of protoplanetary disks around a selection of metal-poor star clusters in the outermost regions of the galaxy. The lack of a protoplanetary disk means a lack of exoplanet-birthing potential and a grim outlook for life to evolve in regions of the galaxy distant from the galactic core.

The conclusion of this 2009 work appears to contradict these most recent findings and the suggestion that advanced alien civilizations may have evolved around metal-poor stars. Whether these stars are the exception rather than the rule, or whether their low metallicity influences the size or visibility of their protoplanetary disks would be an interesting factor to consider.

Although SETI searches have yet to turn up any signal from an advanced alien technology, Kepler is proving that stars — regardless of their metallicity — have the ability to host small rocky worlds. Should life have taken hold on these worlds, then perhaps, some day, we may intercept an interstellar phone call from one of them.

This topic and a myriad of others will be discussed on June 22-24 where the world’s leaders in the field of alien and exoplanet hunting will meet at the Hyatt Santa Clara hotel in California’s Silicon Valley for SETIcon.

UPDATE: After tweeting this article, @spacearcheology retweeted my link with the following comment:

This is something I neglected to consider in the original post. If there are indeed many more small rocky worlds out there — particularly around metal-poor stars that are, by their nature, ancient — why the heck haven’t we detected any ancient extraterrestrial intelligences yet? This has just become the Fermi Paradox PLUS…

Exoplanet Count Tops 700

An artist's impression of a lone exoplanet transiting its parent star. There are now 700 confirmed alien worlds orbiting other stars (ESO)

An artist's impression of a lone exoplanet transiting its parent star. There are now 700 confirmed alien worlds orbiting other stars (ESO)

On Friday, the Extrasolar Planets Encyclopedia registered more than 700 confirmed exoplanets. Although this is an amazing milestone, it won’t be long until the “first thousand” are confirmed.

There are now more than 700 confirmed exoplanets in the database. The latest addition is the planet HD 100655 b.
— announced via the Exoplanet iPhone app

Only two months ago, the encyclopedia — administered by astrobiologist Jean Schneider of the Paris-Meudon Observatory — registered 600 confirmed alien worlds. Since then, there has been a slew of announcements including the addition of a batch of 50 exoplanets by the European Southern Observatory’s (ESO) High Accuracy Radial velocity Planet Searcher (or HARPS) in September.

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.

When an Astrophysicist Needs a Star Map

Stars of the Northern Hemisphere, Ashland Astronomy Studio

Stars of the Northern Hemisphere, Ashland Astronomy Studio

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.

The very cool Ashland Astronomy Studio Star Map can be purchased from Amazon.

Could Kepler Detect Borg Cubes? Why Not.

That's no sunspot.

"That's no sunspot."

Assuming Star Trek‘s Borg Collective went into overdrive and decided to build a huge cube a few thousand miles wide, then yes, the exoplanet-hunting Kepler space telescope should be able to spot it. But how could Kepler distinguish a cube from a nice spherical exoplanet?

With the help of Ray Villard over at Discovery News, he did some digging and found a paper dating back to 2005 — long before Kepler was launched. However, researcher Luc Arnold, of the Observatoire de Haute-Provence in Paris, did have the space telescope in mind when he studied what it would take to distinguish different hypothetical shapes as they passed in front of his theoretical stars.

The big assumption when looking for exoplanets that drift between distant stars and the Earth — events known as “transits” — is that the only shape these detectable exoplanets come in are spheres. Obvious really.

As a world passes in front of its parent star, a circular shadow will form. However, from Earth, we’d detect a slight dimming of the star’s “light curve” during the transit, allowing astronomers to deduce the exoplanet’s orbital period and size.

The transit method has been used to confirm the presence of hundreds of exoplanets so far, and Kepler has found over 1,200 additional exoplanet candidates. But say if astronomers paid closer attention to the shape of the received light curve; spherical objects have a distinct signature, but say if something looked different in the transiting “planet’s” light curve? Well, it could mean that something non-spherical has passed in front of a star. And what does that mean? Well, that would be a pretty convincing argument for the presence of a huge planet-sized artificial structure orbiting another star. Artifical structure = super-advanced alien civilization.

Arnold tested his theory that all manner of shapes could be detected by Kepler, assuming the transiting structure was on the scale of a few thousand miles wide. In this case, Arnold was testing his hypothesis to see whether we could detect an advanced civilization’s “shadow play.” Perhaps, rather than beaming messages by radio waves, an advanced civilization might want to signal their presence — SETI style — by blocking their sun’s light with vast sheets of lightweight material. As the shape passes in front of the star, the slight dimming of starlight would reveal an artificial presence in orbit.

By putting a series of these shapes into orbit, the aliens could create a kind of interstellar Morse code.

Of course, this is a rather “out there” idea, but I find it fascinating that Kepler could detect an alien artifact orbiting a star tens or hundreds of light-years away. Although this research is only considering orbital “billboards,” I quite like the idea that Kepler might also be able to detect a large structure like… I don’t know… a big Borg mothership. Having advanced warning of the presence of an aggressive alien race sitting on our cosmic doorstep — especially ones of the variety that like to assimilate — would be pretty handy.

Publication: Transit Lightcurve Signatures of Artificial Objects, L. Arnold, 2005. arXiv:astro-ph/0503580v1

Screaming Exoplanets: Detecting Alien Magnetospheres

Exoplanets may reveal their location through radio emissions (NASA)

Exoplanets may reveal their location through radio emissions (NASA)

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.

What’s more, the brand new LOw Frequency ARray (LOFAR) radio telescope should be sensitive enough to detect aurorae on Jupiter-like exoplanets, even though the exoplanets themselves are invisible to other detection methods. Nice.

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…

Ingredients for Life on Gliese 581g?

Credit: Lynette Cook

Just in case you haven’t heard, astronomers have released news about an “Earth-like” exoplanet orbiting within the “Goldilocks zone” of a star some 20 light-years away. This is awesome, but does it mean Gliese 581g is habitable? Does it mean life is already slithering across its surface?

Judging by an exuberant claim by Steven Vogt, professor of astronomy and astrophysics at University of California Santa Cruz, one would think we now know there’s life on this strangely familiar world.

“Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say that the chances for life on this planet are 100 percent. I have almost no doubt about it,” Vogt told Discovery News when the announcement broke on Wednesday.

100%?

Why did he say that his personal view was that the chances for life on Gliese 581g are 100%? At first glance, it is easy to see where he’s coming from.

Goldilocks Zone

Firstly, the exoplanet orbits close to a small red dwarf star (called Gliese 581), with a fast-paced orbit of 37 days. This is important as the energy output of a red dwarf is tiny when compared to our Sun (which is a yellow dwarf star, in case you were wondering) — to receive an equivalent amount of heating as the Earth, Gliese 581g needs to be much closer to its star.

Also, it isn’t orbiting too close. It is within the habitable zone (or the “Goldilocks zone,” i.e., a zone that’s not too hot or too cold) of the system. Therefore there’s a high probability that if water is present on its surface, it’s likely to be in liquid form. The presence of liquid water would be exciting as Earth Brand™ life likes liquid water.

Secondly, Gliese 581g is small for an exoplanet discovered thus far. Weighing in at a minimum mass of 3x that of the Earth, it could certainly have some Earth-like qualities. This has another implication; the world has enough gravitational oomph to hold onto an atmosphere — another ingredient that life seems to like (assuming it’s not of the bone-crushing, lead-boiling, Venus-type atmosphere).

It’s Complicated

But there’s a few complications. To be within the habitable zone of its parent star, Gliese 581g will be “tidally locked.” This means that one side of the exoplanet will always be facing the star. On the far side (or, indeed, the “dark side”) it will be cold whilst the near side will always be hot. Having one perpetual day doesn’t sound very Earth-like to me. But there is an upside to this strange orbit.

“This planet doesn’t have days and nights. Wherever you are on this planet, the sun is in the same position all the time. You have very stable zones where the ecosystem stays the same temperature… basically forever,” Vogt said. “If life can evolve, it’s going to have billions and billions of years to adapt to the surface.”

So a tidally-locked planet could have a stable atmosphere and perhaps life could evolve as a result. What could be considered to be a negative has just become a positive.

With all this good news, why wouldn’t life be thriving on this world?

Unknowns and Assumptions

There’s still a lot of unknowns and assumptions being made. For a start, the presence of Gliese 581g was detected by measuring the “wobble” of the star as the exoplanet orbits (its gravity tugs on the star as it circles). Therefore its mass and orbital radius can be derived. But we have no information about its atmosphere; the world doesn’t pass in front (or “transit”) the star from our perspective, so we can’t get a peek into its atmosphere.

Therefore we have zero clue as to whether it even has an atmosphere. It might not have an atmosphere, but then again it could have a very thick atmosphere — two extremes that would would put a stop to any Earth Brand™ life evolving. Also, we have zero clue if there’s any water there, it’s just guesswork that suggests there might be. There’s also the huge unknown as to whether life is ubiquitous in the cosmos or not.

Bread in the Oven

It’s a bit like baking a loaf of bread when you have all the necessary ingredients to make bread, but you have no clue about what quantities to use. Gliese 581g appears to have most of the ingredients for life (and with a few assumptions, it has all the ingredients for life), but we only have a general idea as to what quantities these ingredients come in.

If you threw flour, water and yeast straight into the breadmaker in random quantities, would you get a loaf of bread? What if you forgot to add the yeast?

Gliese 581g is that breadmaker. Unfortunately we have no clue if it can make bread.

For more on this incredible discovery, read Irene Klotz’s Discovery News article: “Earth-Like Planet Can Sustain Life