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at 3:00 AM 0

“It’s more dynamic and alive than Mars,” says UCF planetary scientist Philip Metzger. “The only planet that has more complex geology is the Earth.” The reason Pluto lost its planet status is not valid, according to new research from the University of Central Florida in Orlando.

In 2006, the International Astronomical Union, a global group of astronomy experts, established a definition of a planet that required it to “clear” its orbit, or in other words, be the largest gravitational force in its orbit.

Since Neptune’s gravity influences its neighboring planet Pluto, and Pluto shares its orbit with frozen gases and objects in the Kuiper belt, that meant Pluto was out of planet status. However, in a new study published online Wednesday in the journal Icarus, UCF planetary scientist Philip Metzger, who is with the university’s Florida Space Institute, reported that this standard for classifying planets is not supported in the research literature.

Metzger, who is lead author on the study, reviewed scientific literature from the past 200 years and found only one publication — from 1802 — that used the clearing-orbit requirement to classify planets, and it was based on since-disproven reasoning.

What did NASA's New Horizons discover around Pluto?

He said moons such as Saturn’s Titan and Jupiter’s Europa have been routinely called planets by planetary scientists since the time of Galileo.

“The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be a defined on the basis of a concept that nobody uses in their research,” Metzger said. “And it would leave out the second-most complex, interesting planet in our solar system.” “We now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it’s functionally useful,” he said. “It’s a sloppy definition,” Metzger said of the IAU’s definition. “They didn’t say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit.”

The planetary scientist said that the literature review showed that the real division between planets and other celestial bodies, such as asteroids, occurred in the early 1950s when Gerard Kuiper published a paper that made the distinction based on how they were formed.

However, even this reason is no longer considered a factor that determines if a celestial body is a planet, Metzger said.

Study co-author Kirby Runyon, with Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, said the IAU’s definition was erroneous since the literature review showed that clearing orbit is not a standard that is used for distinguishing asteroids from planets, as the IAU claimed when crafting the 2006 definition of planets.

“We showed that this is a false historical claim,” Runyon said. “It is therefore fallacious to apply the same reasoning to Pluto,” he said. Metzger said that the definition of a planet should be based on its intrinsic properties, rather than ones that can change, such as the dynamics of a planet’s orbit. “Dynamics are not constant, they are constantly changing,” Metzger said. “So, they are not the fundamental description of a body, they are just the occupation of a body at a current era.”

Instead, Metzger recommends classifying a planet based on if it is large enough that its gravity allows it to become spherical in shape.

“And that’s not just an arbitrary definition, Metzger said. “It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body.”

Pluto, for instance, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons, he said.

The Daily Galaxy via University of Central Florida

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at 2:50 AM 0
Webb contains novel technologies that have never previously been flown in space
The US space agency boasts that it will literally "look back in time to see the very first galaxies that formed in the early Universe".

As if those claims were not bold enough, scientists have now surmised that the eventual successor to the world famous and beloved Hubble Space Telescope may - thanks to its 6.5m golden mirror and exquisitely sensitive cameras - have a another extraordinary talent.

The JWST, as it is called, may be able to look for signs of alien life - detecting whether atmospheres of planets orbiting nearby stars are being modified by that life.

Despite this, the project to build it narrowly survived cancellation by the US Government in 2011. That was in no small part down to its (perhaps appropriately) astronomical cost - an estimated $10bn rather than its originally planned $1bn.

Back on Earth, however, astronomers - including the University of Washington team who proposed "life-detection" observations using the telescope - are unerringly thrilled at the prospect of its launch.


How do you detect life on distant planets?
University of Washington astronomer Joshua Krissansen-Totton and his team have looked into whether the telescope could detect signs of what they call "biosignatures" in the atmospheres of planets that are orbiting a nearby star.

"We could do these life-detection observations in the next few years," says Mr Krissansen-Totton.

The basis for this search may lie in JWST being so sensitive to light that it could pick up so-called "atmospheric chemical disequilibrium".

Earth's atmosphere would change if all life was suddenly removed
It may not be a catchy term, but it is an idea with a long heritage, promoted by celebrated scientists James Lovelock and Carl Sagan.

The reasoning is that if all life on Earth disappeared tomorrow, the many gases which make up our atmosphere would undergo natural chemical reactions, and the atmosphere would slowly revert to a different chemical mixture.

It is continually held away from this state by organisms on our planet expelling waste gases as they live.

Because of this, searching for signs of oxygen (or its chemical cousin ozone) has long been thought to be a good way of finding life. But this does rest on the assumption that extraterrestrial life runs by the same biological rules as our own.

It might not. Therefore, assessing atmospheric chemical disequilibrium - looking for other gases and figuring out how far out of kilter from "normal' a planet's atmosphere sits - could be key to finding alien life of any kind.

The chemical make-up of the atmosphere of a planet orbiting another star can be measured in light by carefully measuring the minuscule dip in starlight as the planet passes between us and the star during the planet's orbit. The gases in the planet's atmosphere cause the light reduction to vary with the wavelength - or colour - of light, revealing information about how much of each chemical is present.

Where is the best place to look?
Mr Krissansen-Totton simulated the data that would be obtained if JWST were to look at planets orbiting a small Jupiter-sized star called TRAPPIST-1, about 39.6 light-years away from our Sun. This star caused a sensation in 2017 when it was discovered to host seven Earth-sized planets, several of which could possess liquid water, and hence might be a good bet for hosting life.

The Washington researcher predicts that James Webb could measure the amounts of methane and carbon dioxide in the atmosphere of the fourth planet, TRAPPIST-1e, from the dips in light at wavelengths affected by these gases.

It would be a tough measurement of an unimaginably tiny signal, but Cornell University astronomer Prof Jonathan Lunine, who was not involved in this study, is excited by the prediction, saying "they make the case that this can really be done with JWST".


All seven planets are thought to have Earth-like characteristics

Once the measurement is made, though, Mr Krissansen-Totton explains, "you can then ask the question: do we know of any non-biological processes" that could produce that effect?"

Planetary atmospheres, including our own, he points out, can also be modified by non-biological processes, such as volcanic activity. So, if the atmosphere of TRAPPIST-1e was found to be awry, researchers would then need to rule out any non-biological effects before declaring the existence of extraterrestrial life.

Mr Krissansen-Totton says that "that kind of confirmation is going to require multiple observations, to really make a totally solid case".

"But if we detect something that we don't have an alternative explanation for, I think that would be an incredibly exciting discovery."

Who else will be doing this?
For now, the telescope's golden mirror remains securely locked in a lab in California, and astronomers must continue to wait for these possibilities to be explored.

JWST will be joining a host of new facilities that will subject planets around other stars to some serious scrutiny over the next few decades.

Huge ground-based telescopes in Hawaii and Chile are also planned, and the European Space Agency's UK-led Ariel mission, designed to probe the atmospheres of planets around other stars, will blast off in the late 2020s.

Prof Lunine says: "I think that we're in a remarkable time for understanding our Universe and exploring the cosmos, and James Webb is going to take the next step in that.

"It is going to be truly worth it."

Prof Gillian Wright, principal scientist on the telescope's UK-led Mid-InfraRed instrument, agrees. "We've never had access to something this big in space before," she says.

"To say a telescope will open up new windows on the Universe sounds kind-of cliched, but with James Webb it's really true."

JWST is led by Nasa but is a joint venture with the European and Canadian space agencies. Dr Jonathan Nichols is a planetary scientist from the University of Leicester and a 2018 British Science Association media fellow
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at 7:21 PM 0

Image credit: NASA/JPL-Caltech

The conditions for life surviving on planets entirely covered in water are more fluid than previously thought, opening up the possibility that water worlds could be habitable, according to a new paper from the University of Chicago and Pennsylvania State University.

The scientific community has largely assumed that planets covered in a deep ocean would not support the cycling of minerals and gases that keeps the climate stable on Earth, and thus wouldn’t be friendly to life. But the study, published Aug. 30 in The Astrophysical Journal, found that ocean planets could stay in the “sweet spot” for habitability much longer than previously assumed. The authors based their findings on more than a thousand simulations.

“This really pushes back against the idea you need an Earth clone–that is, a planet with some land and a shallow ocean,” said Edwin Kite, assistant professor of geophysical sciences at UChicago and lead author of the study.

As telescopes get better, scientists are finding more and more planets orbiting stars in other solar systems. Such discoveries are resulting in new research into how life could potentially survive on other planets, some of which are very different from Earth–some may be covered entirely in water hundreds of miles deep.

Because life needs an extended period to evolve, and because the light and heat on planets can change as their stars age, scientists usually look for planets that have both some water and some way to keep their climates stable over time. The primary method we know of is how Earth does it. Over long timescales, our planet cools itself by drawing down greenhouse gases into minerals and warms itself up by releasing them via volcanoes.

But this model doesn’t work on a water world, with deep water covering the rock and suppressing volcanoes.

Kite, and Penn State coauthor Eric Ford, wanted to know if there was another way. They set up a simulation with thousands of randomly generated planets, and tracked the evolution of their climates over billions of years.

“The surprise was that many of them stay stable for more than a billion years, just by luck of the draw,” Kite said. “Our best guess is that it’s on the order of 10 percent of them.”

These lucky planets sit in the right location around their stars. They happened to have the right amount of carbon present, and they don’t have too many minerals and elements from the crust dissolved in the oceans that would pull carbon out of the atmosphere. They have enough water from the start, and they cycle carbon between the atmosphere and ocean only, which in the right concentrations is sufficient to keep things stable.

“How much time a planet has is basically dependent on carbon dioxide and how it’s partitioned between the ocean, atmosphere and rocks in its early years,” said Kite. “It does seem there is a way to keep a planet habitable long-term without the geochemical cycling we see on Earth.”

The simulations assumed stars that are like our own, but the results are optimistic for red dwarf stars, too, Kite said. Planets in red dwarf systems are thought to be promising candidates for fostering life because these stars get brighter much more slowly than our sun–giving life a much longer time period to get started. The same conditions modeled in this paper could be applied to planets around red dwarfs, they said: Theoretically, all you would need is the steady light of a star.
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at 7:17 PM 0
Artist concept of exoplanet GJ 1214b. Credit: NASA

A team of astronomers at the University of Chicago and Grinnell College seeks to change the way scientists approach the search for Earth-like planets orbiting stars other than the sun. They favor taking a statistical comparative approach in seeking habitable planets and life beyond the solar system.

“The nature of proof should not be: ‘Can we point at a planet and say, yes or no, that’s the planet hosting alien life,” said Jacob Bean, associate professor of astronomy and astrophysics at UChicago. “It’s a statisical exercise. What can we say for an ensemble of planets about the frequency of the existence of habitable environments, or the frequency of the existence of life on those planets?”

The standard approach of researching exoplanets, or planets that orbit distant stars, has entailed studying small numbers of objects to determine if they have the right gases in the appropriate quantities and ratios to indicate the existence of life. But in a recent paper with co-authors Dorian Abbot and Eliza Kempton in the Astrophysical Journal Letters, Bean describes the need “to think about the techniques and approaches of astronomy in this game–not as planetary scientists studying exoplanets.”

“Nature has provided us with huge numbers of planetary systems,” said Kempton, an assistant professor of physics at Grinnell College in Iowa. “If we survey a large number of planets with less detailed measurements, we can still get a statistical sense for how prevalent habitable environments are in our galaxy. This would give us a basis for future, more detailed surveys.”

Kempton and Bean attest to the challenges of making detailed observations of a potentially Earth-like planet. Together they have previously studied the super-Earth known as GJ 1214b, an exoplanet with a mass greater than Earth’s but less than gas giants such as Neptune and Uranus. GJ 1214b turned out to be quite cloudy, which prevented them from determining the composition of its atmosphere.

“A large statistical study will allow us to look at many planets,” Kempton said. “If any single object proves to be particularly challenging to observe, like GJ 1214b, that won’t be a major loss to the observing program on the whole.”


Artist impression of Kepler. Credit: NASA


Kepler observatory a game-changer

The inspiration for the paper stemmed from Bean’s membership on the Science and Technology Definition Team that is assessing the potential for a new space telescope, NASA’s proposed Large UV/Optical/Infrared Survey (LUVOIR).

One of LUVOIR’s scientific priorities is the search for Earth-like planets. During one team meeting, Bean and his colleagues listed all the properties of a potentially habitable exoplanet that they need to measure and how they would go about obtaining the data. Given the current state of technology, Bean concluded that it’s unlikely scientists will be able to confirm an individual exoplanet as suitable for life or whether life is actually there.

Nevertheless, astronomers have gathered an impressive haul of exoplanetary data from NASA’s Kepler space observatory, which has operated since 2009.

“Kepler completely changed the game,” Bean said. “Instead of talking about a few planets or a few tens of planets, all of a sudden we had a few thousand planet candidates. They were planet candidates because Kepler couldn’t definitely prove that the signal it was seeing was due to planets.”

The standard approach has been to take additional observations for each candidate to rule out possible false positive scenarios, or to detect the planet with a second technique.

“That’s very slow going. One planet at a time, a lot of different observations,” Bean noted. But an alternative is to make statistical calculations for the probability of false positives among these thousands of exoplanet candidates. That new approach led directly to a good understanding of the frequency of exoplanets of different sizes. For example, scientists now can say that the frequency of super-Earth-type planets is 15 percent, plus or minus 5 percent.

Role of spectroscopy

Spectroscopic studies play a key role in characterizing exoplanets. This involves determining the composition of a planetary atmosphere by measuring its spectra, the distinctive radiation that gases absorb at their own particular wavelengths. Bean and his co-authors suggest focusing on what can be learned from measuring the spectra of a large ensemble of terrestrial exoplanets.

Spectroscopy may, for example, help exoplanetary researchers verify a phenomenon called the silicate weathering feedback, which acts as a planetary thermostat. Through silicate weathering, the amount of atmospheric carbon dioxide varies according to geologic processes. Volcanoes emit carbon dioxide into the atmosphere, but rain and chemical reactions that occur in rocks and sediments also remove the gas from the atmosphere.

Rising temperatures would put more water vapor into the atmosphere, which then rains out, increasing the amount of dissolved carbon dioxide that chemically interacts with the rocks. This loss of carbon dioxide from the atmosphere has a cooling effect. But as a planet begins to cool, rock weathering slows and the amount of carbon dioxide gradually builds from its volcanic sources, which causes rising temperatures.

Global-scale observations suggest that Earth has experienced silicate-weathering feedback. But attempts to verify that the process is operating today on the scale of individual river basins has proven difficult.

“The results are very noisy. There’s no clear signal,” Abbot said. “It would be great to have another independent confirmation from exoplanets.”

All three co-authors are interested in fleshing out the details of experiments they proposed in their paper. Abbot plans to calculate how much carbon dioxide would be necessary to keep a planet habitable at a range of stellar radiation intensities while changing various planetary parameters. He also will assess how well a future instrument would be able to measure the gas.

“Then we will put this together to see how many planets we would need to observe to detect the trend indicating a silicate-weathering feedback,” Abbot explained.

Bean and Kempton, meanwhile, are interested in detailing what a statistical census of biologically significant gases such as oxygen, carbon dioxide and ozone could reveal about planetary habitability.

“I’d like to get a better understanding of how some of the next-generation telescopes will be able to distinguish statistical trends that indicate habitable–or inhabited–planets,” Kempton said.

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at 4:03 AM 0
An artist’s impression of a habitable exoplanet. Seasonal changes and the presence of disequilibrium gases in such a planet’s atmosphere could indicate the existence of life there.
Credit: NASA Ames/SETI Institute/JPL-hCaltec

Biosignatures that vary in time and atmospheric gases that shouldn't exist without life to replenish them could be two possible ways to detect life on exoplanets.


Finding any life that might exist on other planets is extremely challenging. Even in our own Solar System, where we can send probes and orbiters to worlds of interest such as Mars, it is difficult to assess if any microbial life is, or was ever, present. When studying exoplanets, we can only look at the starlight shining through a planet's atmosphere in the hope that it will reveal absorption or emission lines that indicate gases produced by life. Detailed analyses of the atmospheres of exoplanets is still mostly in the realm of future telescopes, such as the James Webb Space Telescope (JWST), but understanding what to look for is an important step in the hunt for life on other planets.

Oxygen is produced by photosynthesis and is commonly thought to be a potential biosignature on other worlds, although it is also possible for oxygen to be produced from abiotic sources. Similarly, methane is produced by life and is a potential biomarker, but can also be produced by other means. Now, two recent papers discuss new ways of looking for biosignatures by studying how life can influence a planet’s atmosphere. [NASA's TESS Exoplanet-Hunting Mission in Pictures]

A paper by Stephanie Olson at the University of California, Riverside, and colleagues, discusses how seasonal changes in the atmosphere caused by life could be used as a biosignature. The second paper is by Joshua Krissansen-Totton at the University of Washington, along with Olson and David Catling, and looked at potential biosignatures produced by atmospheric gases that can only co-exist in the presence of life.

The changing seasons

Signals from an exoplanet that vary over time, such as with the seasons, could help to rule out false positives or negatives that occur in single snapshot observations. By understanding how atmospheric gases vary over the course of a year on Earth, it will help inform scientists about what signals to look for on other planets.


"Rather than simply recognizing that a planet hosts life, we may be able to say something about how the activities of its biosphere vary in space and time," says Olson.

Seasonality in the Earth's atmosphere arises because of the interactions between the biosphere and the varying solar radiation reaching Earth at different points in its orbit. Seasonal variations shift the balance between two different reactions: photosynthesis and aerobic respiration. Photosynthesis occurs as carbon dioxide and water react to become organic matter and oxygen, and aerobic respiration causes the reverse reaction, producing carbon dioxide and water. The maximum production of oxygen occurs during the summer months when temperatures are warm.

The researchers examined the seasonal variations in carbon dioxide on Earth, a signal that could be detectable on other planets assuming that life elsewhere is also carbon-based. Carbon dioxide is an important atmospheric component on habitable worlds due to the role it plays in climate regulation via weathering.

They found that the seasonal carbon dioxide (CO2) signal would be dominated by land-based ecosystems, which are in direct contact with the atmosphere, indicating that CO2variability might not be detectable on ocean worlds. This is seen on Earth, where the ocean-dominated Southern Hemisphere has a weaker CO2 variability signal than the Northern Hemisphere. Carbon dioxide seasonality would be difficult to detect on other planets, but it is a powerful indicator of the presence of life since it is unlikely to occur on planets with an ocean unless life is present. [Exoplanet Discovery: The 7 Earth-Sized Planets of TRAPPIST-1 in Pictures]

They also looked at the scenario of an exoplanet that is an analog of the early-Earth, where life existed but where there was still very little oxygen in the atmosphere. Weak oxygen signals are difficult to detect, but a varying ozone signature (ozone is a molecule built from three oxygen atoms) might be more visible in the spectrum of an exoplanet. Such a signal is more likely to be detected for a planet with less oxygen than the present-day Earth because ozone can create a stronger signal than oxygen.


"Seasonality would be difficult to detect for a planet resembling the present-day Earth, at least in the case of oxygen," explains Olson. "The reason is that baseline levels of oxygen are really high today, and so small seasonal fluctuations are very challenging to measure at our planets surface, and would be even more so on a distant planet."

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