Saturn, the sixth planet from the Sun, is known for its beautiful rings, but NASA’s Cassini spacecraft has revealed that the Rings may also play a crucial role in heating the planet’s atmosphere. In particular, the discovery reveals the rings of Saturn are emitting heat due to the icy particles colliding with each other inside the planet’s magnetic field.
This surprising discovery was made using data collected by NASA’s Cassini spacecraft, which orbited Saturn between 2004 and 2017. The researchers used Cassini’s Radio and Plasma Wave Science (RPWS) instrument to measure the electrically charged particles that are present in Saturn’s magnetic field. They found that the rings were emitting energy in the form of radio waves, which suggests that they were heating up the planet’s atmosphere.
The researchers believe that the heating of Saturn’s atmosphere could also explain why the planet’s upper atmosphere is so much warmer than expected. The temperature at the top of Saturn’s atmosphere is about -270 degrees Celsius, which is colder than the surface temperature of the planet. However, the researchers found that the area directly above the rings was actually much warmer, with temperatures of around -170 degrees Celsius.
One of the reasons Saturn’s atmosphere is so warm is due to the planet’s distance from the Sun. While Saturn is approximately nine times farther from the Sun than Earth, its upper atmosphere is hotter than expected. The researchers believe that the Rings are crucial to explaining this phenomenon because they are providing energy to the planet’s atmosphere.
The exact mechanism behind this heating process is still unknown, but the researchers believe that it is due to the charged particles in Saturn’s magnetic field interacting with the icy particles in the Rings. As these particles collide with one another, they generate energy in the form of heat and radio waves, which then heats up the atmosphere above the Rings.
The discovery has significant implications for our understanding of Saturn’s atmosphere and could also have wider implications for our understanding of other planets with rings. Saturn is the only planet in our solar system with such distinctive features, and this research suggests that the Rings are also crucial to its atmosphere.
Furthermore, this research could also help us understand how planets in other solar systems heat their atmospheres. Many of the newfound exoplanets are believed to have rings, and this research suggests that these rings could also play a role in heating the planet’s atmosphere.
In conclusion, the discovery that the Rings of Saturn may help to heat up the planet’s atmosphere is a significant development in our understanding of the dynamics of the sixth planet from the Sun. While there is still much to learn about this process, this research could ultimately help us to better understand how planets form and evolve. With the help of instruments such as Cassini’s RPWS, we can continue to unravel the mysteries of the cosmos and the celestial bodies within it.
Frequent contributor to Fox News Steven Milloy retweeted a Politico story about climate change to suggest that CO2 won’t kill Earth because Venus is made of CO2 — the only trouble is humans don’t live on Venus, as far as we know.
Milloy is no stranger to ignoring accurate and verified scientific truths. A lawyer and frequent commentator for Fox News, he refers to himself as a libertarian thinker and runs a twitter account called @JunkScience through which he ironically, but not facetiously, often peddles what mosts scientists would refer to as junk science. His close financial and organizational ties to tobacco and oil companies have been the subject of criticism from a number of sources going back to the early 2000s, as Milloy has consistently disputed the scientific consensus on climate change and the health risks of second-hand smoke. Having close ties to tobacco and oil, it’s not difficult to understand why.
Among the topics Milloy has addressed are what he believes to be false claims regarding DDT, global warming, Alar, breast implants, second-hand smoke, ozone depletion, and mad cow disease. This time, however, he attempts to equate planet Earth with planet Venus, saying that CO2 won’t destroy the Earth because Venus is largely made up of CO2.
DeFazio on climate: "This is the existential threat to the future of the planet."
Insanity.
For comparison, the atmosphere Venus is 96.5% CO2 — and the planet is still there.
The obvious problem to scientists (and most people with a high school science education) is that humans don’t live on Venus, and couldn’t since it is so darn hot, hailing an average temperature of 864 degrees Fahrenheit.
It’s obvious that Milloy is being paid to promote bad science in an effort to persuade Fox News watchers into believing that climate change is a hoax. The trick he uses here is to make it seem like people who believe in man-induced global warming through greenhouse gases such as carbon dioxide think the Earth will cease to exist with too much CO2. That isn’t what climate change scientists and activists think at all.
On the contrary, climate change scientists and activists are concerned about human and animal life will cease to exist — the way it doesn’t exist on Venus.
The danger in having to explain this to people is that it’s easier to look at things Milloy’s way. Despite it being wrong, lazy thinkers will read what he tweets and hear what he says on Fox News without doing anymore research or thinking on the matter. When people say convincing things with authority, it usually doesn’t matter if what they’re saying is true or not.
For the first time in history, NASA has discovered a total of eight planets orbiting a distant star that is much like our Sun, the space agency announced on Thursday.
The star, Kepler-90, is 2,545 light-years from Earth and located in the Draco constellation. It is the first star known to humans to support just as many planets as the known Solar System, but what is exciting to many is that astronomers believe that this is in fact only the beginning of a long line of discoveries to come out of our latest technological advances.
For a time, researchers had known that a total of seven planets were orbiting Kepler-90, but Google Artificial Intelligence had a hand in discovering the eighth planet when it looked into archival data originally obtained by NASA’s Kepler telescope, designed specifically to look for planets.
With the idea of eventually differentiating among exoplanets, Christopher Shallue, senior software engineer at Google AI in California, and Andrew Vanderburg, astronomer and NASA Sagan postdoctoral fellow at the University of Texas, Austin, trained a computer how to differentiate between images of cats and dogs, refining their approach to identify exoplanets in Kepler data based on the change in light when a planet passed in front of its star. The neural network learned to identify these by using signals that had been vetted and confirmed in Kepler’s planet catalog. Ninety-six percent of the time, it was accurate.
A new study shows that an atmosphere was produced around the ancient Moon, 3 to 4 billion years ago, when intense volcanic eruptions spewed gases above the surface faster than they could escape to space. The study, supported by NASA’s Solar System Exploration Research Virtual Institute, was published in Earth and Planetary Science Letters.
When one looks up at the Moon, dark surfaces of volcanic basalt can be easily seen to fill large impact basins. Those seas of basalt, known as maria, erupted while the interior of the Moon was still hot and generating magmatic plumes that sometimes breached the lunar surface and flowed for hundreds of kilometers. Analyses of Apollo samples indicate those magmas carried gas components, such as carbon monoxide, the ingredients for water, sulfur, and other volatile species.
In new work, Dr. Debra H. Needham, Research Scientist of NASA Marshall Space Flight Center, and Dr. David A. Kring, Universities Space Research Association (USRA) Senior Staff Scientist, at the Lunar and Planetary Institute (LPI), calculated the amounts of gases that rose from the erupting lavas as they flowed over the surface and showed that those gases accumulated around the Moon to form a transient atmosphere. The atmosphere was thickest during the peak in volcanic activity about 3.5 billion years ago and, when created, would have persisted for about 70 million years before being lost to space.
The two largest pulses of gases were produced when lava seas filled the Serenitatis and Imbrium basins about 3.8 and 3.5 billion years ago, respectively. The margins of those lava seas were explored by astronauts of the Apollo 15 and 17 missions, who collected samples that not only provided the ages of the eruptions, but also contained evidence of the gases produced from the erupting lunar lavas.
NASA’s Needham says, “The total amount of H2O released during the emplacement of the mare basalts is nearly twice the volume of water in Lake Tahoe. Although much of this vapor would have been lost to space, a significant fraction may have made its way to the lunar poles. This means some of the lunar polar volatiles we see at the lunar poles may have originated inside the Moon.”
David Kring notes, “This work dramatically changes our view of the Moon from an airless rocky body to one that used to be surrounded by an atmosphere more prevalent than that surrounding Mars today.” When the Moon had that atmosphere, it was nearly 3 times closer to Earth than it is today and would have appeared nearly 3 times larger in the sky.
This new picture of the Moon has important implications for future exploration. The analysis of Needham and Kring quantifies a source of volatiles that may have been trapped from the atmosphere into cold, permanently shadowed regions near the lunar poles and, thus, may provide a source of ice suitable for a sustained lunar exploration program. Volatiles trapped in icy deposits could provide air and fuel for astronauts conducting lunar surface operations and, potentially, for missions beyond the Moon.
Over the past decade, the search for volatiles within the Moon and on the surface of the Moon has intensified. Those volatiles may hold clues about the material that accreted to form the Earth and Moon and, thus, our planetary origins. The volatiles may also provide the in-situ resources needed for sustained lunar surface activities that may follow the development of NASA’s new Orion crew vehicle and a Gateway structure that may orbit the Moon. In addition, robotic assets, like NASA’s Resource Prospector, are being developed to explore the nature and distribution of volatile deposits that might be suitable for scientific analysis and recovery. Based on the new results of Needham and Kring, those assets may be recovering ice that is partially composed of volatiles erupted from volcanic fissures over 3 billion years ago.
The new research was initiated from the LPI-Johnson Space Center’s (JSC) Center for Lunar Science and Exploration, led by Kring and supported by NASA’s Solar System Exploration Research Virtual Institute. Needham is a former postdoctoral researcher at the LPI. The LPI is operated for NASA by Universities Space Research Association (USRA).
For NASA’s Saturn explorer, the end will come all too quickly.
Cassini, NASA’s explorer of Saturn, remaining life is now measured in just a few days. Coming up on September 12, just three days before NASA’s veteran Saturn explorer takes a dive into the planet’s atmosphere, the spacecraft will whip around the hazy moon Titan in a slingshot maneuver that will seal its fate.
During these final days, Cassini will take one last look around. Onboard cameras will snap pictures of Titan and its hydrocarbon lakes, Saturn’s innermost rings, the bizarre hexagon-shaped jet stream at Saturn’s north pole, and other targets. On the evening of September 14, Cassini will send this last photo album to Earth, about 1.4 billion kilometers away, and the engineers at NASA’s Jet Propulsion Laboratory in Pasadena will post them online.
After that, no more pictures will be taken. But seven other instruments will continue to gather data on the chemical composition of Saturn’s atmosphere, its gravity and magnetic fields, its innermost radiation belts, and its rings—for as long as they can. “We’ll be transmitting the science data back almost as fast as we gather it,” says Tom Burk, Cassini’s attitude control team lead.
Scientists forecast rain storms of solid diamonds on two of the solar system’s most interesting planets
The obvious question any entrepreneur might ask is how do you mine these diamonds? In short, you don’t. It would take highly advanced space drones, the likes of which not even SpaceX is ready for yet, let alone the cost of getting there and back.
But that doesn’t make the idea of diamonds raining down on a distant planet any less of a spectacular discovery, igniting space-nerd radars everywhere.
According to the scientists who ran the experiment, the diamonds form in hydrocarbon-rich oceans of “slush” found around the solid cores of these two gad giants. According to the Washington Post,
Scientists have long speculated that the extreme pressures in this region might split those molecules into atoms of hydrogen and carbon, the latter of which then crystallize to form diamonds. These diamonds were thought to sink like rain through the ocean until they hit the solid core.
Cassini is the most sophisticated space probe ever built. Launched in 1997 as a joint NASA/European Space Agency mission, it took seven years to journey to Saturn. It’s been orbiting the sixth planet from the sun ever since, sending back data of immense scientific value and images of magnificent beauty.
Cassini now begins one last campaign. Dubbed the Grand Finale, it will end on Sept. 15, 2017 with the probe plunging into Saturn’s atmosphere, where it will burn up. Although Saturn was visited by three spacecraft in the 1970s and 1980s, my fellow scientists and I couldn’t have imagined what the Cassini space probe would discover during its sojourn at the ringed planet when it launched 20 years ago.
A huge storm churning across the face of Saturn. At the time this image was taken, 12 weeks after the storm began, it had completely wrapped around the planet. NASA/JPL-Caltech/SSI, CC BY
A planet of dynamic change
Massive storms periodically appear in Saturn’s cloud tops, known as Great White Spots, observable by Earthbound telescopes. Cassini has a front-row seat to these events. We have discovered that just like Earth’s thunderstorms, these storms contain lightning and hail.
Cassini has been orbiting Saturn long enough to observe seasonal changes that cause variations in its weather patterns, not unlike the seasons on Earth. Periodic storms often appear in late summer in Saturn’s northern hemisphere.
In 2010, during northern springtime, an unusually early and intense storm appeared in Saturn’s cloud tops. It was a storm of such immensity that it encircled the entire planet and lasted for almost a year. It was not until the storm ate its own tail that it eventually sputtered and faded. Studying storms such as this and comparing them to similar events on other planets (think Jupiter’s Great Red Spot) help scientists better understand weather patterns throughout the solar system, even here on Earth.
Having made hundreds of orbits around Saturn, Cassini was also able to deeply investigate other features only glimpsed from Earth or earlier probes. Close encounters with Saturn’s largest moon, Titan, have allowed navigators to use the moon’s gravity to reorient the probe’s orbit so that it could swing over Saturn’s poles. Because of Saturn’s strong magnetic field, the poles are home to beautiful Aurorae, just like those of Earth and Jupiter.
Saturn’s six-sided vortex at Saturn’s north pole known as ‘the hexagon.’ This is a superposition of images taken with different filters, with different wavelengths of light assigned colors. NASA/JPL-Caltech/SSI/Hampton University, CC BY
Cassini has also confirmed the existence of a bizarre hexagon-shaped polar vortex originally glimpsed by the Voyager mission in 1981. The vortex, a mass of whirling gas much like a hurricane, is larger than the Earth and has top wind speeds of 220 mph.
Home to dozens of diverse worlds
Cassini discovered that Saturn has 45 more moons than the 17 previously known – placing the total now at 62.
The largest, Titan, is bigger than the planet Mercury. It possesses a dense nitrogen-rich atmosphere with a surface pressure one and a half times that of Earth’s. Cassini was able to probe beneath this moon’s cloud cover, discovering rivers flowing into lakes and seas and being replenished by rain. But in this case, the liquid is not water, but rather liquid methane and ethane.
False-color image of Ligeia Mare, the second largest known body of liquid on Saturn’s moon Titan. It’s filled with liquid hydrocarbons. NASA/JPL-Caltech/ASI/Cornell, CC BY
That’s not to say that water is not abundant there – but it’s so cold on Titan (with a surface temperature of -180℃) that water behaves like rock and sand. Although it has all the ingredients for life, Titan is essentially a “frozen Earth,” trapped at that moment in time before life could form.
The sixth-largest moon of Saturn, Enceladus, is an icy world about 300 miles in diameter. And for me, it’s the site of the Mission’s most spectacular finding.
The discovery started humbly, with a curious blip in magnetic field readings during the first flyby of Enceladus in 2004. As Cassini passed over the moon’s southern hemisphere, it detected strange fluctuations in Saturn’s magnetic field. From this, the Cassini magnetometer team inferred that Enceladus must be a source of ionized gas.
Intrigued, they instructed the Cassini navigators to make an even closer flyby in 2005. To our amazement, the two instruments designed to determine the composition of the gas that the spacecraft flies through, the Cassini Plasma Spectrometer (CAPS) and the Ion and Neutral Mass Spectrometer (INMS), determined that Cassini was unexpectedly passing through a cloud of ionized water. Emanating from cracks in the ice at Enceladus’ south pole, these water plumes gush into space at speeds up to 800 mph.
I am on the team that made the positive identification of water, and I have to say it was the most thrilling moment in my professional career. As far as Saturn’s moons were concerned, everyone thought all of the action would be at Titan. No one expected small, unassuming Enceladus to harbor any surprises.
Geologic activity happening in real time is quite rare in the solar system. Before Enceladus, the only known active world beyond Earth was Jupiter’s moon Io, which possesses erupting volcanoes. To find something akin to Old Faithful on a moon of Saturn was practically unimaginable. The fact that it all started with someone noticing an odd reading in the magnetic field data is a wonderful example of the serendipitous nature of discovery.
The geyser basin at the south pole of Enceladus, with its water plumes illuminated by scattered sunlight. NASA/JPL-Caltech/Space Science Institute, CC BY
The story of Enceladus only becomes more extraordinary. In 2009, the plumes were directly imaged for the first time. We now know that water from Enceladus comprises the largest component of Saturn’s magnetosphere (the area of space controlled by Saturn’s magnetic field), and the plumes are responsible for the very existence of Saturn’s vast E-ring, the second outermost ring of the planet.
More amazingly, we now know that beneath the crust of Enceladus is a global ocean of liquid saltwater and organic molecules, all being heated by hydrothermal vents on the seafloor. Detailed analysis of the plumes show they contain hydrocarbons. All this points to the possibility that Enceladus is an ocean world harboring life, right here in our solar system.
NASA at Saturn: Cassini’s Grand Finale.
When Cassini plunges into the cloud tops of Saturn later this year, it will mark the end of one of the most successful missions of discovery ever launched by humanity.
Scientists are now considering targeted missions to Titan, Enceladus or possibly both. One of the most valuable lessons one can take from Cassini is the need to continue exploring. As much as we learned from the first spacecraft to reach Saturn, nothing prepared us for what we would find with Cassini. Who knows what we will find next?
Ever since enthusiasm started growing over the possibility that there could be a ninth major planet orbiting the sun beyond Neptune, astronomers have been busy hunting it. One group is investigating four new moving objects found by members of the public to see if they are potential new solar system discoveries. As exciting as this is, researchers are also making discoveries that question the entire prospect of a ninth planet.
One such finding is our discovery of a minor planet in the outer solar system: 2013 SY99. This small, icy world has an orbit so distant that it takes 20,000 years for one long, looping passage. We found SY99 with the Canada-France-Hawaii Telescope as part of the Outer Solar System Origins Survey. SY99’s great distance means it travels very slowly across the sky. Our measurements of its motion show that its orbit is a very stretched ellipse, with the closest approach to the sun at 50 times that between the Earth and the sun (a distance of 50 “astronomical units”).
The new minor planet loops even further out than previously discovered dwarf planets such as Sedna and 2013 VP113. The long axis of its orbital ellipse is 730 astronomical units. Our observations with other telescopes show that SY99 is a small, reddish world, some 250 kilometres in diameter, or about the size of Wales in the UK.
SY99 is one of only seven known small icy worlds that orbit beyond Neptune at remarkable distances. How these “extreme trans-Neptunian objects” were placed on their orbits is uncertain: their distant paths are isolated in space. Their closest approach to the sun is so far beyond Neptune that they are thought to be “detached” from the strong gravitational influence of the giant planets in our solar system. But at their furthest points, they are still too close to be nudged around by the slow tides of the galaxy itself.
Planet Nine could explain why the few known extreme trans-Neptunian objects seem to be clustered together in space. The diagram was created using WorldWide Telescope. Caltech/R. Hurt (IPAC)
It’s been suggested that the extreme trans-Neptunian objects could be clustered in space by the gravitational influence of a “Planet Nine” that orbits much further out than Neptune. This planet’s gravity could lift out and detach their orbits – constantly changing their tilt. But this planet is far from proven.
In fact, its existence is based on the orbits of only six objects, which are very faint and hard to discover even with large telescopes. They are therefore prone to odd biases. It’s a bit like looking down into the deep ocean at a school of fish. The fish swimming near the surface are clearly visible. But the ones even only a meter down are fainter and murky, and take quite a lot of peering to be certain. The great bulk of the school, in the depths, is completely invisible. But the fish at the surface and their behaviour betray the existence of a whole school.
The biases mean SY99’s discovery can’t prove or disprove the existence of a Planet Nine. However, computer models do show that a Planet Nine would be an unfriendly neighbour to tiny worlds like SY99: its gravitational influence would starkly change its orbit – throwing it from the solar system entirely, or poking it into an orbit so highly inclined and distant that we wouldn’t be able to see it. SY99 would have to be one of an utterly vast throng of small worlds, continuously being sucked in and cast out by the planet.
The alternative explanation
But it turns out that there are other explanations. Our study based on computer modelling, accepted for publication in the Astronomical Journal, hint at the influence of an idea from everyday physics called diffusion. This is a very common type of behaviour in the natural world. Diffusion typically explains the random movement of a substance from a region of higher concentration to one of lower concentration – such as the way perfume drifts across a room.
We showed that a related form of diffusion can cause the orbits of minor planets to change from an ellipse that is initially only 730 astronomical units on its long axis to one that is as big as 2,000 astronomical units or bigger – and change it back again. In this process, the size of each orbit would vary by a random amount.
When SY99 comes to its closest approach every 20,000 years, Neptune will often be in a different part of its orbit on the opposite side of the solar system. But at encounters where both SY99 and Neptune are close, Neptune’s gravity will subtly nudge SY99, minutely changing its velocity. As SY99 travels out away from the sun, the shape of its next orbit will be different.
The long axis of SY99’s ellipse will alter, becoming either larger or smaller, in what physicists call a “random walk”. The orbit change takes place on truly astronomical time scales. It diffuses over the space of tens of millions of years. The long axis of SY99’s ellipse would change by hundreds of astronomical units over the 4.5 billion-year history of the solar system.
Several other extreme trans-Neptunian objects with smaller orbits also show diffusion, on a smaller scale. Where one goes, more can follow. It’s entirely plausible that the gradual effects of diffusion act on the tens of millions of tiny worlds orbiting in the near fringe of the Oort cloud (a shell of icy objects at the edge of the solar system). This gentle influence would slowly lead some of them to randomly shift their orbits closer to us, where we see them as extreme trans-Neptunian objects.
However, diffusion won’t explain the distant orbit of Sedna, which has its closest point too far out from Neptune for it to change its orbit’s shape. Perhaps Sedna gained its orbit from a passing star, aeons ago. But diffusion could certainly be bringing in extreme trans-Neptunian objects from the inner Oort cloud – without the need for a Planet Nine. To find out for sure, we’ll need to make more discoveries in this most distant region using our largest telescopes.
They are both found in the Afar Region of Ethiopia and are part of the East African Rift System – an active tectonic plate boundary that’s splitting apart plates at a rate of 7 mm per year. The combination of this area’s geology and environment make it a uniquely extreme place to do research. In collaboration with the Europlanet research team, I am investigating the geological and biological aspects of the Danakil Depression.
Our aim is to study microbes, specifically extremophiles – organisms that thrive in extreme environments. They can live in hot springs, acidic fields, salty lakes and polar ice caps – conditions that would kill humans, animals, and plants. Their existence suggests that life can develop mechanisms to withstand physical and chemical conditions like those on the planet Mars.
There’s no other natural environment like it. What we have found at the site is a combination of extreme physico-chemical parameters. Toxic gases saturate the air, the pH is extremely acidic and saline and metal concentrations are very high.
In these extreme ecosystems we expect to find microbial life in the form of extremophiles, polyextremophiles and potentially new forms of polyextremophiles – these are extremophilic organisms that can tolerate, or adapt, to a combination of physico-chemical parameters.
Harsh environment
This harsh environment was created by the splitting apart of the old African Plate into two plates – the Somali and Nubian Plates. In millions of years, these two plates will be definitively separated and a new ocean basin will form.
Much of the 40km by 10 km Danakil Depression lies between 150-100m below sea level. It’s therefore one of the lowest land areas on Earth. The Dallol volcano, in the northern part of the Danakil Depression, was formed in 1926 by a phreatic eruption. This is when groundwater is heated by magma – essentially, a steam eruption without the lava ejection. Dallol has an elevation of approximately 50m below sea level.
Barbara Cavalazzi collects samples at Dallol.
The Depression is known as the hottest place on Earth. It’s classified as a hyperarid climatic zone and is consistently hot throughout the year. In the Dallol, because of the area’s geothermal activity, the average daily temperature is 45°C. I have registered a temperature there of 55°C – when I had to stop working! The region’s precipitation ranges is very low with an average annual rainfall of only 100-200 mm. In the dry areas of South Africa there would be an average annual rainfall of at least 464mm.
Geothermally heated groundwater rises from the Earth’s crust to the surface, accumulating in the Dallol crater. This creates spectacular and colourful hot springs that are extremely acidic and salty. The area is also characterised by toxic sulphur and chlorine vapours as a result of natural degassing volcanic processes.
What can survive
Living organisms tend to be sensitive to drastic changes in their environments. The cells that make them up can be seriously compromised in extreme physical (relating to temperature, desiccation, radiation, and pressure) and (geo)chemical (such as salinity, pH or heavy metals) conditions.
So what could survive in the Danakil’s harsh environment?
After a detailed study of the area, we have determined that there’s DNA evidence of microbial life. Life that, because of the similar extreme salty environment with volcanic origin, could be what’s surviving on Mars.
The microorganisms able to survive such extreme conditions must be a group of prokaryotes. All living things consist of two cell types: prokaryotes and eukaryotes. Organisms whose cells lack a nucleus and have DNA floating loosely in the liquid centre of the cell are prokaryotes. These are the most common and most ancient forms of life on earth.
What these microorganisms need is liquid water, metabolically suitable carbon, energy, and nutrient sources.
Barbara Cavalazzi, Professor in Geobiology and Astrobiology at the Biological, Geological, and Environmental Sciences-BiGeA of the University of Bologna, Italy, and visiting lecturer at University of Johannesburg, South Africa., University of Bologna
Scientists have discovered seven Earth-sized planets, so tightly packed around a dim star that a year there lasts less than two weeks. The number of planets and the radiation levels they receive from their star, TRAPPIST-1, make these worlds a miniature analogue of our own Solar System.
The excitement surrounding TRAPPIST-1 was so great that the discovery was announced with an article in Nature accompanied by a NASA news conference. In the last two decades, nearly 3,500 planets have been found orbiting stars beyond our Sun, but most don’t make headlines.
How likely are we really to find a blue marble like our Earth among these new worlds?
Earth 2.0?
We still know little about these planets with certainty, but initial clues look enticing.
All seven worlds complete an orbit in between 1.5 and 13 days. So closely are they huddled that a person standing on one planet might see the neighbouring worlds in the sky even larger than our Moon. The short years place the planets closer to their star than any planet sits to the Sun. Happily, they avoid being baked by TRAPPIST-1 because it is incredibly dim.
TRAPPIST-1 is a small ultracool dwarf star with a luminosity roughly 1/1000th that of the Sun. Comparing the two at Wednesday’s news conference, lead author of the Nature paper, Michaël Gillon, said that if the Sun were scaled to the size of a basketball, TRAPPIST-1 would be a puny golf ball. The resulting paltry amount of heat means that three of the seven TRAPPIST-1 planets actually receive similar amounts of radiation as Venus, Earth and Mars.
This alternative Solar System does look like a compact version of our own, but does TRAPPIST-1 include an Earth 2.0?
Artists impression of the seven TRAPPIST-1 worlds, compared to our solar system’s terrestrial planets. NASA/JPL-Caltech
Here’s the good news first.
The seven siblings are all Earth-sized, with radii between three quarters and one times that of our home planet and masses that range from roughly 50% to 150% of Earth’s (the mass of the outermost world remains uncertain).
Because all are smaller than 1.6 times Earth’s radius, the seven TRAPPIST-1 planets are likely to be rocky worlds, not gaseous Neptunes. TRAPPIST-1d, e and f are within the star’s temperate region — aka the “Goldilocks zone” where it’s not too hot and not too cold — where an Earth-like planet could support liquid water on its surface.
The orbits of the six inner planets are nearly resonant, meaning that in the time it takes for the innermost planet to orbit the star eight times, its outer siblings make five, three and two orbits.
Such resonant chains are expected around stars where the planets have moved from where they originally formed. This migration occurs when the planets are still young and embedded in the star’s gaseous planet-forming disc. As the gravity of the young planet and the gas disc pull on one another, the planet’s orbit can change, usually moving towards the star.
If multiple planets are in the system, their gravity also pulls on one another. This nudges the planets into resonant orbits as they migrate through the gas disc. The result is a string of resonant planets close to the star, just like that seen encircling TRAPPIST-1.
Being born far from the star offers a couple of potential advantages. Dim stars like TRAPPIST-1 are irritable when young, emitting flares and high radiation that may sterilise the surface of nearby planets. If the TRAPPIST-1 system did indeed form further away and migrate inwards, its worlds may have avoided getting fried.
Originating where temperatures are colder would also mean the planets formed with a large fraction of ice. As the planets migrate inwards, this ice could melt into an ocean. This notion is supported by the estimated densities of the planets, which are low enough to suggest volatile-rich compositions, like water or a thick atmosphere.
Not an Earth?
Since our search for extraterrestrial life focuses on the presence of water, melted icy worlds seem ideal.
But this may actually bode ill for habitability. While 71% of the Earth’s surface is covered by seas, water makes up less than 0.1% of our planet’s mass. A planet with a high fraction of water may become a water world: all ocean and no exposed land.
Deep water could also mean there’s a thick layer of ice on the ocean floor. With the planet’s rocky core separated from both air and sea, no carbon-silicate cycle could form – a process that acts as a thermostat to adjust the level of warming carbon dioxide in the air on Earth.
If the TRAPPIST-1 planets can’t compensate for different levels of radiation from their star, the temperate zone for the planet shrinks to a thin strip. Any little variation, from small ellipicities in the planet’s orbit to variations in the stellar brightness, could turn the world into a snowball or baked desert.
Jupiter’s moon Io, is in resonance with moons Europa and Ganymede, and its tidal heating powers its volcanoes. NASA/JPL/University of Arizona
Even if the oceans were sufficiently shallow to avoid this fate, an icy composition might produce a very strange atmosphere. On the early Earth, air was spewed out in volcanic plumes. If a TRAPPIST-1 planet’s interior is more akin to a giant comet than to a silicate-rich Earth, the air expelled risks being rich in the greenhouse gases of ammonia and methane. Both trap heat at the planet’s surface, meaning the best location for liquid water might actually be in a region cooler than the “Goldilocks zone”.
Finally, the TRAPPIST-1 system’s orbits are problematic. Situated so close to the star, the planets are likely in tidal lock – with one face permanently turned towards the star – resulting in perpetual day on one side and everlasting night on the other.
Not only would this be weird to experience, the associated extremes of temperatures could also evaporate all water and collapse the atmosphere if the planet’s winds are unable to redistribute heat.
Also, even a small ellipticity in the planets’ seemingly circular orbits could power a second kind of warmth, called tidal heating, making the planets into Venus-like hothouses. Slight elongations in the planet’s path around its star would cause the pull from the star’s gravity to strengthen and weaken during its year, flexing the planet like a stress ball and generating tidal heat.
This process occurs on three of Jupiter’s largest moons whose mildly elliptical paths are caused by resonant orbits similar to the TRAPPIST-1 worlds. In Europa and Ganymede, the flexing heat allows subsurface liquid oceans to exist. But Jupiter’s innermost moon, Io, is the most volcanic place in our Solar System.
If the TRAPPIST-1 planets’ orbits are similarly bent, they could turn out to be sweltering.
The view from here
So how will we ever know what the TRAPPIST-1 planets are really like? To investigate the possible scenarios, we need to take a look at the atmosphere of the TRAPPIST-1 siblings.
TRAPPIST-1 was named for the Belgian 60cm TRAnsiting Planets and Planetesimal Small Telescope in Chile that detected the star’s first three planets last year (it also happens to be the name of a type of Belgian beer). As the name suggests, both the original three worlds and four new planetary siblings were discovered using the transit technique; the tiny dip in starlight as the planets passed between the star and the Earth.
Transiting makes the planets excellent candidates for the next generation of telescopes with their ability to identify molecules in the planet’s air as starlight passes through the gas. The next five years may therefore give us the first real look at a rocky planet with a very different history to anything in our Solar System.
Thomas Zurbuchen, associate administer of the Science Mission Directorate at NASA, declared the discovery of TRAPPIST-1 as, “A leap forward to answering ‘are we alone?’”.
But the real treasure of TRAPPIST-1 is not the possibility that the planets may be just like the one we call home; it’s the exciting thought that we might be looking at something entirely new.
