7 Earth-Size Planets Identified in Orbit Around a Dwarf Star

[SolarpunkFan]

https://www.nytimes.com/2017/02/22/scie ... -nasa.html

Not just one, but seven Earth-size planets that could potentially harbor life have been identified orbiting a tiny star not too far away, offering the first realistic opportunity to search for biological signs of alien life outside of the solar system.

The planets orbit a dwarf star named Trappist-1, about 40 light years, or about 235 trillion miles, from Earth. That is quite close, and by happy accident, the orientation of the orbits of the seven planets allows them to be studied in great detail.

One or more of the exoplanets — planets around stars other than the sun — in this new system could be at the right temperature to be awash in oceans of water, astronomers said, based on the distance of the planets from the dwarf star.

“This is the first time so many planets of this kind are found around the same star,” said Michael Gillon, an astronomer at the University of Liege in Belgium and the leader of an international team that has been observing Trappist-1.

They could even discover convincing evidence of aliens.

“I think that we have made a crucial step toward finding if there is life out there,” said Amaury H.M.J. Triaud, an astronomer at the University of Cambridge in England and another member of the research team. “Here, if life managed to thrive and releases gases similar to that we have on Earth, then we will know.”

The findings appear Wednesday in the journal Nature.

Telescopes on the ground now and the Hubble Space Telescope in orbit will be able to discern some of the molecules in the planetary atmospheres. The James Webb Telescope, scheduled to launch next year, will peer at the infrared wavelengths of light, ideal for studying the dimmer longer wavelength light coming from Trappist-1.

Comparisons among the different conditions of the seven will also be revealing.

“The Trappist-1 planets make the search for life in the galaxy imminent,” said Sara Seager, an astronomer at the Massachusetts Institute of Technology who was not a member of the research team. “For the first time ever, we don’t have to speculate. We just have to wait and then make very careful observations and see what is in the atmospheres of the Trappist planets.”

Even if the planets all turn out to be lifeless, gaining an understanding of the constraints for when life can exist or cannot would also be important new knowledge.

Astronomers always knew other stars must have planets, but until a couple of decades ago, they had not been able to spot them. Now they have confirmed more than 3,400, according to the Open Exoplanet Catalog.

While the Trappist planets are about the size of Earth — give or take 25 percent in diameter — the star is very different from our sun.

Trappist-1, named after a robotic telescope in Chile’s Atacama Desert that the astronomers initially used to study the star, is what astronomers call an “ultracool dwarf,” with only one-twelfth the mass of the sun and a surface temperature of 4,150 degrees Fahrenheit, much cooler than the 10,000 degrees of heat radiating from the sun. Trappist is a shortening of Transiting Planets and Planetesimals Small Telescope.

Until the last few years, scientists looking for life elsewhere in the galaxy have focused on finding Earth-size planets around sun-like stars. But it is difficult to pick out the light of a planet from the glare of a bright star. Small dim dwarfs are much easier to study.

Last year, astronomers announced the discovery of an Earth-size planet around Proxima Centauri, the closest star at 4.24 light years away. That discovery was made using a different technique that does not allow for study of the atmosphere.

Trappist-1 periodically dimmed slightly, indicating that a planet might be passing in front of the star, blocking part of the light. From the shape of the dips, the astronomers calculate the size of the planet.

Trappist-1’s light dipped so many times that the astronomers concluded, in research reported last year, that there were at least three planets around the star. Telescopes from around the world then also observed Trappist-1 as did NASA’s Kepler Space Telescope.

Kepler observed Trappist-1 nearly around the clock for 20 days, capturing 34 transits. Together with the ground observations, the scientists calculated not three planets, but seven. The planets are too small and too close to the star to be photographed directly.

If placed within our solar system, all seven would lie within the orbit of Mercury, and they circle the star quickly. The innermost completes an orbit in just 1.5 days. The farthest one completes an orbit in 12.35 days. That makes the planetary system more like the moons of Jupiter than a larger planetary system like our solar system.

“They form a very compact system,” Dr. Gillon said, “the planets being pulled close to each other and very close to the star.”

In addition, the orbital periods of the inner six are in almost exact integer ratios, which astronomers describe as “resonant.” That suggests that the planets formed farther away from the star and then were all gradually pulled inward, Dr. Gillon said.

Because the planets are so close to a cool star, their surfaces could be at the right temperatures to have water flow, considered one of the essential ingredients for life.

The fourth, fifth and six planets orbit in the star’s “habitable zone,” where the planets could be awash in oceans. So far that is just speculation, but by measuring which wavelengths of light are blocked by the planet, scientists will be able to figure out what gases float in the atmospheres of the seven planets.

So far, they have confirmed for the two innermost planets that they are not enveloped in hydrogen. That means they are rocky like Earth, ruling out the possibility that they were mini-Neptune gas planets that are prevalent around many other stars.

Because the planets are so close to Trappist-1, they have quite likely become “gravitationally locked” to the star, always with one side of the planets facing the star, much as it is always the same side of Earth’s moon facing Earth. That would mean one side would be warmer, but an atmosphere would distribute heat, and the scientists said that would not be an insurmountable obstacle for life.

For a person standing on one of the planets, it would be a dim environment, with perhaps only about one-two hundredth the light that we see from the sun on Earth, Dr. Triaud said. (That would still be brighter than the moon at night.) But the star would be far bigger. On Trappist-1f, the fourth planet, the star would be three times as wide as the sun seen from Earth.

As for the color of the star, “we had a debate about that,” Dr. Triaud said.

Some of the scientists expected a deep red, but with most of the star’s light emitted at infrared wavelengths and out of view of human eyes, perhaps a person would “see something more salmon-y,” Dr. Triaud said.

If observations reveal oxygen in a planet’s atmosphere, that could point to photosynthesis of plants — but that would not be conclusive. But oxygen together with methane, ozone and carbon dioxide, particularly in certain proportions, “would tell us there is life with 99 percent confidence,” Dr. Gillon said.

Astronomers expect that a few decades of technological advances are needed before similar observations can be made of Earthlike planets around larger, brighter sunlike stars.

Dr. Triaud said that if there is life around Trappist-1, “Then it’s good we didn’t wait too long. If there isn’t, then we have learned something quite deep about where life can emerge.”

The discovery might also mean that scientists who have been searching for radio signals from alien civilizations might also have been looking in the wrong places if most habitable planets orbit dwarfs, which live far longer than larger stars like the sun.

“If you’re looking for complex biology, intelligent aliens that might take a long time to evolve from pond scum, older could be better,” said Seth Shostak, an astronomer at the Seti Institute in Mountain View, Calif. “It seems a good bet that the majority of clever beings populating the universe look up to see a dim, reddish sun hanging in their sky. And at least they wouldn’t have to worry about sun block.”

Dr. Shostak said the Seti Institute is now using a huge telescope array to scrutinize 20,000 red dwarfs. “This result is kind of a justification for that project,” he said.

Interesting.

[The Romulan Republic]

I love stories like this.

I'm reminded of the setting for "Firefly"/Serenity, which had a whole pack of Earth-like planets in a single system that was probably not too far from Earth (given that it was reached by colonists with STL).

I think I'm going to start nicknaming this system "The 'Verse".

Also, the idea that most inhabited worlds might be around dwarf stars, that ours' is an exception in this respect, is quite intriguing.

[Galvatron]

I love stories like this.

I'm reminded of the setting for "Firefly"/Serenity, which had a whole pack of Earth-like planets in a single system that was probably not too far from Earth (given that it was reached by colonists with STL).

I think I'm going to start nicknaming this system "The 'Verse".

Also, the idea that most inhabited worlds might be around dwarf stars, that ours' is an exception in this respect, is quite intriguing.

On the other hand, the bigger stars have gigantic habitable zones...



I wonder how long they can live though. Dwarf stars have those insanely long lifespans that could easily allow for the gradual development of intelligent life on planets in their own habitable zones.

[Eternal_Freedom]

Bigger stars live absurdly short lifespans compared to the Sun or dwarfs. The rule of thumb we learned at university was lifetime of star = )lifetime of sun)/(mass^3), solar masses of course.

Henec a 2 solar mass star only lives about 1.25 billion years. So IMO, unless planets around massive stars have been terraformed, it is extremely unlikely that they would be habitable. There is also the point that brighter stars emit much more UV than the Sun does, which is probably a bad thing.

[Guardsman Bass]

It's a pretty neat discovery, and those planets are incredibly close together. Only downside is that the star probably sucks for habitability - a small red dwarf like TRAPPIST-1 would spit out flares, x-rays, major changes in luminosity whenever it has a bout of sunspots, and worst of all the long pre-main sequence phase when it would have roasted any planets in its habitable zone (Venus equivalents at best, total loss of atmosphere at worst).

That said, the star is relatively close and dim, so it's a good candidate for follow-up to try and measure the planets' atmospheres (if any). The word "dim" being the key point there - TRAPPIST-1 is about as small and low-mass as a star can get while still igniting fusion. The threshold is something like 75-80 times the Mass of Jupiter to get it, and this star has 83 times Jupiter's mass (it's also quite young).

[SpottedKitty]

Also, the idea that most inhabited worlds might be around dwarf stars, that ours' is an exception in this respect, is quite intriguing.

Our star is a yellow dwarf, so we're not really an exception to that. The news is certainly food for thought; considering there are more dwarf stars than everything else put together, a massive increase in discovered exoplanets seems to be waiting only for us to develop sensitive enough detection techniques. (The BBC report on this included a sample of the light curves; the dips signifying transiting planets aren't very obvious.)

I wonder... with the outermost planet orbitting in only a few weeks, are they sure they haven't yet seen any gas or ice giants much further out?

[wautd]

I'm calling dibs. I like beer and I love trappist

[Galvatron]

Relatively old news, but it may have gone unnoticed over the past few months by some of you...

Two Trillion Galaxies, at the Very Least

The scale of the universe, already unfathomable, just became even more so: There are about 10 times as many galaxies as previously thought.

The new number, two trillion galaxies, is the result of work led by Christopher J. Conselice, an astrophysicist at the University of Nottingham in England, published last week in The Astrophysical Journal.

The team analyzed sky surveys by the Hubble Space Telescope and other instruments able to see far away, and therefore far back, through about 13 billion years of time. The astronomers formed three-dimensional models to measure the number of galaxies at different times.

Because not even the Hubble or large Earth-based telescopes can see the oldest, faintest galaxies, they also did some mathematical work to come up with two trillion.

“It’s much bigger than anyone would have guessed,” Dr. Conselice said. “And the real number could be even higher.”

Previous estimates were that there were perhaps 200 billion galaxies in the observable universe. One might well ask — what difference does it make? Or put another way, once you get past a couple of hundred billion galaxies, who’s counting?

But the finding has important implications for understanding how the universe has evolved.

The researchers found that most of the oldest galaxies were low in mass, similar to some of the small “satellite” galaxies near our own Milky Way, and that there were about 10 times fewer low-mass galaxies today. That suggests that over billions of years, galaxies have been colliding and joining together.

The study also suggests how important the more powerful James Webb Space Telescope, set to be launched in 2018, will be.

“It will be able to study these galaxies that we’re just barely detecting — these lower-mass galaxies that are really the first galaxies of the universe,” Dr. Conselice said.

That's a lot of galaxies, which no doubt means a lot of dwarf stars too. I'm sure we're all alone though.

[The Romulan Republic]

The odds of their being zero intelligent alien life in a universe of two trillion galaxies or more, when Earth-like planets appear to be quite common, are ludicrous.

The real question is weather any is close enough for us to ever contact it. Which is a question with a number of unanswered variables.

[SolarpunkFan]

The odds of their being zero intelligent alien life in a universe of two trillion galaxies or more, when Earth-like planets appear to be quite common, are ludicrous.

The real question is weather any is close enough for us to ever contact it. Which is a question with a number of unanswered variables.

So far we know ones that are roughly similar in mass and are likely common. But that's about it for now.

As for good old Fermi's question? I've had an interest in it for a while.

Try getting the book If the Universe Is Teeming with Aliens ... Where Is Everybody?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life by Stephen Webb. The book suggests that there are a lot of small stumbling blocks that lead to a rarity of technological civilizations (though not life and possibly not even intelligent life) via a process similar to the Sieve of Eratosthenes.

This is some good food for thought too: http://www.projectrho.com/public_html/r ... mi_Paradox

Sorry for the off-topic stuff. Fermi's Paradox is a major interest of mine.

[The Romulan Republic]

Its funny.

I remember reading stuff as a child, published maybe a few decades ago, speculating weather their might be other planets in other solar systems.

How far we've come. And to think that we might actually soon be able to detect evidence of life around one of these worlds.

Is it really petty of me that I don't want arguably the most significant discovery in human history to occur under Trump's Presidency?

[Terralthra]

My personal answer to the Fermi paradox is a combination of efficiency and Snowden's response. First, beaming massively powerful, collimated radio signals into space is wasteful as shit. Here on Terra, we only did it for a couple decades of broadcasts before making things into narrow-beam networks because the power requirements if we broadcasted all 900-some channels would be ridiculous, let alone internet traffic. Second, Snowden's point is that any reasonably well-encrypted datastream is indistinguishable from random noise, by definition: any pattern or regularity to the datastream is a fulcrum against which one can lever to decrypt it. Combine 800 streams that look like noise from every direction with the inverse square law, and the result is exactly what we see: low-volume noise and static up and down the radio bands useful for interstellar communication.

[Iroscato]

I'm sure we're all alone though.

What on Earth (ha!) could possibly make you think such a thing?

[Simon_Jester]

Terralthra, the only question then is, why is everyone and their cousin Fred beaming big intense encrypted broadcast radio signals up into the night sky?

The only real point in using broadcast radio is for signals that anyone can read.

If communication security (for encryption) or efficiency (for data compression) are concerns, they'd be better off using something like a communications laser that doesn't waste as much energy and isn't as easy for an enemy to intercept.

Some of the most intense signals ever sent up into the night sky by Earth were things like the beams from radar dishes- which aren't encrypted and would be very obviously artificial from the point of view of an alien pointing a radio telescope in our general direction. By contrast, as technology advances we actually spend less and less energy on such broadcasts.

[Terralthra]

Terralthra, the only question then is, why is everyone and their cousin Fred beaming big intense encrypted broadcast radio signals up into the night sky?

The only real point in using broadcast radio is for signals that anyone can read.

Nonsense. If sending an encrypted stream to a ship whose precise location is being guarded, a tight-beam laser communication is a vector you can trace. A broadcast signal is...not.

Also, there are plenty of natural phenomena putting out noise in the radio bands. No need for artificial means to explain all of it. The energy/encryption arguments are explanation for why alien civilization communications blend into the background noise, not an argument that they make up all of it.

If communication security (for encryption) or efficiency (for data compression) are concerns, they'd be better off using something like a communications laser that doesn't waste as much energy and isn't as easy for an enemy to intercept.

Some of the most intense signals ever sent up into the night sky by Earth were things like the beams from radar dishes- which aren't encrypted and would be very obviously artificial from the point of view of an alien pointing a radio telescope in our general direction. By contrast, as technology advances we actually spend less and less energy on such broadcasts.

Yes, true, but we...don't send those out any more. We'd have to be pointing a radio telescope at an alien civilization's planetary system during just the tiny window where they have early warning radar. Unlikely, to say the least. Plus, over the course of lightyears, even a comm laser spreads out an awful lot.

[LaCroix]

The longer you think about Fermi's paradox, the Zoo hypothesis becomes more plausible...

[Ziggy Stardust]

To the OP: Incredibly exciting news. I'm very curious what the tidal patterns would be on one of these planets (assuming of course the existence of large bodies of liquid water). While the OP article notes they are probably gravitationally locked with respect to their star, other articles I've read online indicate that the planets themselves are so close together that you would be able to see the other planets in the sky during the day a la the Earth's moon. Depending on the exact distances between all of the planets, and the configuration of their relative orbits with respect to the star, you could potentially see some very interesting seasonal tidal patterns.

[Rhadamantus]

To the OP: Incredibly exciting news. I'm very curious what the tidal patterns would be on one of these planets (assuming of course the existence of large bodies of liquid water). While the OP article notes they are probably gravitationally locked with respect to their star, other articles I've read online indicate that the planets themselves are so close together that you would be able to see the other planets in the sky during the day a la the Earth's moon. Depending on the exact distances between all of the planets, and the configuration of their relative orbits with respect to the star, you could potentially see some very interesting seasonal tidal patterns.

Tides would be strong. To be more specific, stronger than Io on b, and comparable on c. On d, a decent part of land will survive a tidal cycle. On e and onward, they're just crazy strong, only enough to make oceans unnavigable, not submerge mountains.

[Rhadamantus]

I love stories like this.

I'm reminded of the setting for "Firefly"/Serenity, which had a whole pack of Earth-like planets in a single system that was probably not too far from Earth (given that it was reached by colonists with STL).

I think I'm going to start nicknaming this system "The 'Verse".

Also, the idea that most inhabited worlds might be around dwarf stars, that ours' is an exception in this respect, is quite intriguing.

On the other hand, the bigger stars have gigantic habitable zones...



I wonder how long they can live though. Dwarf stars have those insanely long lifespans that could easily allow for the gradual development of intelligent life on planets in their own habitable zones.

Millions of years, which isn't nearly enough for planets to finish forming, let alone develop life.

[Rhadamantus]

By my best guess, b and c should be hot enough to undergo a runaway greenhouse spiral. But they also are exposed to 1% of the uv dose on earth, so I think that they wouldn't lose their water, and so might have supercritical water seas (more likely on c than b), with tides miles high. Which would be interesting.

[SpottedKitty]

A couple of people have mentioned tides; they're going to be really, really weird. Solar tides will be hefty, but (if the planets actually are rotationally locked) they won't move — the high tides will point towards and away from the sun. Any water worlds might be downright odd-looking; e.g. in Larry Niven's Known Space, the planet Jinx (a super-Earth orbiting a gas giant, I think) is described as "banded like an easter egg" with airless tidal bulges, a hothouse Venus-like middle, and rings of Earthlike conditions between them.

I'd hate to try working out tide tables for these planets; overlaid on the solar tides will be separate tides for each of the other planets as they approach and recede. And yes, those tides will slightly enormous, as the whole system (according to the BBC report) is so compact it would fit well inside Mercury's orbit., so they will regularly be coming very close together.

It's complicated enough here on Earth, with only the overlaid solar and lunar tides — high tides are unusually high when they reinforce, unusually low when they oppose. (There are measurable tides from some of the other planets, mostly Jupiter, but they're swamped by the big two.)

[Rhadamantus]

A couple of people have mentioned tides; they're going to be really, really weird. Solar tides will be hefty, but (if the planets actually are rotationally locked) they won't move — the high tides will point towards and away from the sun. Any water worlds might be downright odd-looking; e.g. in Larry Niven's Known Space, the planet Jinx (a super-Earth orbiting a gas giant, I think) is described as "banded like an easter egg" with airless tidal bulges, a hothouse Venus-like middle, and rings of Earthlike conditions between them.

I'd hate to try working out tide tables for these planets; overlaid on the solar tides will be separate tides for each of the other planets as they approach and recede. And yes, those tides will slightly enormous, as the whole system (according to the BBC report) is so compact it would fit well inside Mercury's orbit., so they will regularly be coming very close together.

It's complicated enough here on Earth, with only the overlaid solar and lunar tides — high tides are unusually high when they reinforce, unusually low when they oppose. (There are measurable tides from some of the other planets, mostly Jupiter, but they're swamped by the big two.)

In practice, though, the planets are likely to have slightly eccentric orbits, which would makes tides move a little.

[SpottedKitty]

In practice, though, the planets are likely to have slightly eccentric orbits, which would makes tides move a little.

Maybe, maybe not. Look at many of the larger/closer moons of Jupiter and Saturn; their orbits are either pretty much fixed, or vary in a regular pattern, because they're in resonance — just like the Trappist-1 planets. It's the resonance that holds the orbits where they are, similar to the way orbits in L4 and L5 Lagrangian points are semi-stable.