New research using data collected by the European Southern Observatory (ESO) has revealed that a little-known exoplanet called K2-18b could well be a scaled-up version of Earth.

Image: K2-18b and its neighbor, newly discovered K2-18c, orbit the red-dwarf star k2-18 locataed 111 light years away in the constellation Leo. Illustration by Alex Boersma

Just as exciting, the same researchers also discovered for the first time that the planet has a neighbor.

“Being able to measure the mass and density of K2-18b was tremendous, but to discover a new exoplanet was lucky and equally exciting,” says lead author Ryan Cloutier, a PhD student in U of T Scarborough’s Centre for Planet Science, U of T’s Department of Astronomy and Astrophysics, and Université de Montréal Institute for research on exoplanets (iREx).

Both planets orbit K2-18, a red-dwarf star located about 111 light years away in the constellation Leo. When the planet K2-18b was first discovered in 2015, it was found to be orbiting within the star’s habitable zone, making it an ideal candidate to have liquid surface water, a key element in harboring conditions for life as we know it.

The data set used by the researchers came from the High Accuracy Radial Velocity Planet Searcher (HARPS) using the ESO’s 3.6m telescope at La Silla Observatory, in Chile. HARPS allows for measurements of radial velocities of stars, which can be affected by the presence of nearby planets, to be taken with the highest accuracy currently available. The instrument makes it possible to detect very small planets orbiting those stars.

K2-18b: 'Super-Earth' that could host alien life

In order to figure out whether K2-18b was a scaled-up version of Earth ( mostly rock ), or a scaled-down version of Neptune ( mostly gas ), researchers had to first figure out the planet’s mass, using radial velocity measurements taken with HARPS.

“If you can get the mass and radius, you can measure the bulk density of the planet and that can tell you what the bulk of the planet is made of,” says Cloutier.

After using a machine-learning approach to figure out the mass measurement, Cloutier and his team were able to determine the planet is either a mostly rocky planet with a small gaseous atmosphere – like Earth, but bigger – or a mostly water planet with a thick layer of ice on top of it.

“With the current data, we can’t distinguish between those two possibilities,” he says. 

“But with the James Webb Space Telescope (JWST) we can probe the atmosphere and see whether it has an extensive atmosphere or it’s a planet covered in water.”

The JWST, which will be launched in 2019, will be instrumental in collecting a range of data for studying the solar system, early universe and exoplanets.

“There’s a lot of demand to use this telescope, so you have to be meticulous in choosing which exoplanets to look at,” says René Doyon, a co-author on the paper who is also the principal investigator for NIRISS, the Canadian Space Agency instrument on board JWST.

“K2-18b is now one of the best targets for atmospheric study, it’s going to the near top of the list.”

It was while looking through the data of K2-18b that Cloutier noticed something unusual. In addition to a signal occurring every 39 days from the rotation of K2-18, and one taking place every 33 days from the orbit of K2-18b, he noticed a different signal occurring every nine days.

“When we first threw the data on the table we were trying to figure out what it was. You have to ensure the signal isn’t just noise, and you need to do careful analysis to verify it, but seeing that initial signal was a good indication there was another planet,” Cloutier says.

Cloutier collaborated with an international team of researchers, including his supervisor U of T Scarborough Associate Professor Kristen Menou from the Centre for Planetary Sciences, and from the Observatoire Astronomique de l’Université de Genève, the Institute for research on exoplanets (iREx), Université de Grenoble, and Universidade do Porto.

While the newly described planet K2-18c is closer to its star, and probably too hot to be in the habitable zone, like K2-18b it also appears to be a Super-Earth meaning it has a mass similar to Earth. Cloutier, who had set the goal of discovering a new exoplanet within his PhD, considers himself very lucky to have discovered it in this dataset.

“It wasn’t a eureka moment because we still had to go through a checklist of things to do in order to verify the data. Once all the boxes were checked it sunk in that, wow, this actually is a planet.”

The research, which received support from the Natural Sciences and Research Council of Canada (NSERC) and the Institute for Research on Exoplanets, will be published in the journal Astronomy and Astrophysics.

PDF copy of the Study: Characterization of the K2-18 multi-planetary system with HARPS: A habitable zone super-Earth and discovery of a second, warm super-Earth on a non-coplanar orbit

Source: Don Campbell, University Of Toronto

The discovery of an eighth planet circling the distant star Kepler-90 by University of Texas at Austin astronomer Andrew Vanderburg and Google’s Christopher Shallue overturns our solar system’s status as having the highest number of known planets. We’re now in a tie.

The newly discovered Kepler-90i — a sizzling hot, rocky planet orbiting its star once every 14.4 days — was found using computers that “learned” to find planets in data from NASA’s Kepler space telescope. Kepler finds distant planets beyond the solar system, or exoplanets, by detecting the minuscule change in brightness when a planet transits (crosses in front of) a star.

Vanderburg, a NASA Sagan fellow at UT Austin, and Shallue, a Google machine learning researcher, teamed up to train a computer to learn how to identify signs of an exoplanet in the light readings from distant stars recorded by Kepler. Similar to the way neurons connect in the human brain, this “neural network” sifted through the Kepler data to identify the weak transit signals from a previously missed eighth planet orbiting Kepler-90, a sun-like star 2,545 light-years from Earth in the constellation Draco.

“For the first time since our solar system planets were discovered thousands of years ago, we know for sure that our solar system is not the sole record holder for the most planets,” Vanderburg said.

Kepler-90 is a Sun-like star, but all of its eight planets are scrunched into the equivalent distance of Earth to the Sun. The inner planets have extremely tight orbits with a “year” on Kepler-90i lasting only 14.4 days. In comparison, Mercury’s orbit is 88 days. Consequently, Kepler-90i has an average surface temperature of 800 degrees Fahrenheit, and is not a likely place for life as we know it. The structure of the Kepler-90’s system hints that the eight planets around Kepler-90 may have formed more spread out, like the planets in our own solar system, and then somehow migrated to the orbits we see them in today. Credits: NASA/Ames Research Center/Wendy Stenzel

Other planetary systems, though, would probably hold more promise for life than Kepler-90’s system, which packs all eight planets closer to the host star than Earth is to the sun. In our solar system, only Mercury and Venus orbit between our planet and our sun. About 30 percent larger than Earth, Kepler-90i is so close to its star that its average surface temperature is thought to exceed 800 degrees Fahrenheit, on a par with Mercury. The outermost planet, Kepler-90h, is a gas giant that is about the size of Jupiter, circling with a “year” of 331.6 days.

“The Kepler-90 star system is like a mini version of our solar system. You have small planets inside and big planets outside, but everything is scrunched in much closer,” Vanderburg said.

The research paper reporting this finding has been accepted for publication in The Astronomical Journal.

The idea to apply a neural network to Kepler data came from Shallue, a senior software engineer at Google AI, a research team at the search-engine giant in Mountain View, California. Shallue became interested in exoplanet discovery after learning that astronomy, like other branches of science, is rapidly becoming inundated with data as the technology for collecting data from space advances.

This graphic shows that a small area around the Kepler-90 system, on the left, has been searched by the Kepler space telescope. Compared to our solar system, where we know of planets farther out, it is possible that Kepler-90 has even more planets. If planets (in the blue area) do exist, they probably would not have transited enough times while Kepler was watching for us to know they were there. Credits: NASA/Ames Research Center/Wendy Stenzel

“Machine learning really shines in situations where there is so much data that humans can’t search it for themselves,” Shallue said.

Kepler’s four-year data set, for example, consists of about 2 quadrillion possible orbits of planets. To verify the most promising signals of planets, automated tests, or sometimes human eyes, are typically used, but often the weakest signals are missed during this process. So, Shallue and Vanderburg thought there could be some more interesting exoplanet discoveries lurking in the data.

The two developed a neural network to search Kepler data for new planets. First, they trained the neural network to identify transiting exoplanets in a set of 15,000 previously vetted signals from the Kepler exoplanet catalog. Then, with the neural network having “learned” to detect the pattern of a transiting exoplanet, the researchers pointed their model at 670 star systems that already had multiple known planets and searched for weaker signals. Their assumption was that multiple-planet systems would be the best places to look for more exoplanets.

Kepler-90 had already made its mark in 2013 as the first seven-planet system identified with Kepler, but the signal from the eighth planet was so weak it was missed by previous methods.

“We got lots of false positives of planets but also potentially more real planets,” Vanderburg said. “It’s like sifting through rocks to find jewels. If you have a finer sieve, then you will catch more rocks, but you might catch more jewels as well.”

Kepler-90i wasn’t the only jewel this neural network sifted out. In the Kepler-80 system, they found a sixth planet. This one, the Earth-size Kepler-80g, and four of its neighboring planets form what is called a “resonant chain,” where the planets are locked by their mutual gravity in a rhythmic orbital dance. The result is an extremely stable system, similar to the seven planets in the TRAPPIST-1 system, so precisely balanced that the length of Kepler-80g’s year could be predicted with mathematics.

This work was performed in part under contract with the California Institute of Technology/Jet Propulsion Laboratory, funded by NASA through the Sagan Fellowship Program and executed by the NASA Exoplanet Science Institute.

Source: University of Texas

Image on the top: The Kepler-90 planets have a similar configuration to our solar system with small planets found orbiting close to their star, and the larger planets found farther away. In our solar system, this pattern is often seen as evidence that the outer planets formed in a cooler part of the solar system, where water ice can stay solid and clump together to make bigger and bigger planets. The pattern we see around Kepler-90 could be evidence of that same process happening in this system. Credits: NASA/Ames Research Center/Wendy Stenzel

Building a submarine gets tricky when the temperature drops to -300 Fahrenheit and the ocean is made of methane and ethane.

Washington State University researchers are working with NASA to determine how a submarine might work on Titan, the largest of Saturn’s many moons and the second largest in the solar system. The space agency plans to launch a real submarine into Titan seas in the next 20 years.

The researchers re-created a Titan ocean in a laboratory. They have published a paper on their work in the journal, Fluid Phase Equilibria.

Titan is of particular interest to researchers because it is similar to earth in one important way, it holds liquid. Unlike almost anywhere else in the solar system, the moon’s surface includes oceans, rivers and clouds, and like on earth, it can rain. But, instead of water, the hydrological cycle is based on methane.

Because of the possible lessons it could provide here on Earth, NASA has been studying Saturn and its moons for more than a decade with data collected from the Cassini spacecraft.

The submarine that the agency is designing will have to operate autonomously. It will need to study atmospheric and ocean conditions, move around sea beds, and hover at or below the surface. The engineering is even trickier because, unlike the nearly homogeneous water in earth-based oceans, the concentration of ethane and methane can vary dramatically in the Titan oceans and change the liquid’s density properties.

This is a WSU Methane-ethane Titan effervescence diagram. Washington State University

Ian Richardson, a former graduate student in the School of Mechanical and Materials Engineering, got the chance to tackle how NASA might build a submarine for the extreme conditions. In WSU’s cryogenic lab, which studies materials at very cold temperatures, Richardson re-created the atmosphere of Titan and tested how a small heated machine might work under such conditions.

NASA’s design for a robotic submarine to explore the methane/ethane seas of Titan would arrive sometime in the 2040s to investigate the moon’s largest sea – Kraken Mare. (Click to enlarge) Image Credit: NASA/NIAC

Richardson, who holds a bachelor’s degree in mechanical engineering from WSU, has had a longtime interest in space and space exploration technologies. He was WSU’s first-ever recipient of a NASA Space Technology Research Fellowship, which included an internship at NASA’s Glenn Research Center in Cleveland, Ohio. It was while working as an intern on a separate problem that a NASA scientist approached him with the problem of designing a submarine for Titan.

A diagram showing operational components and scientific instruments of the Titan sub. (Click to enlarge) Image Credit: NASA/NIAC

“My research just took a right turn, and I went with it,” said Richardson. “It’s a crazy experiment, and I never thought I would have had this opportunity. It’s been a very fun and challenging experimental design problem.”

The WSU research team built a test chamber that housed the liquid mixture at very cold temperatures to simulate the seas of Titan. They added a two-inch, cylinder-shaped cartridge heater that would approximate the heat that a submarine would create.

Kraken Mare, Titan’s largest sea, is the body in black and blue that sprawls from just below and to the right of the north pole down to the bottom. Credits: NASA/JPL-Caltech/ASI/USGS

One of the biggest challenges for researchers was understanding bubbles in the Titan seas. Add a submarine powered by a heat-producing machine into the very cold Titan liquid, and nitrogen bubbles will form. Too many bubbles would make it hard to maneuver the ship, see, take data and manage ballast systems.

The next big problem, said Richardson, was getting a video in difficult conditions. Their study was conducted at 60 pounds per square inch of pressure and nearly -300 degrees Fahrenheit. Richardson’s group engineered a solution using an optical device called a borescope and video camera that could withstand the low temperatures and high pressures to visualize what was going on within the test chamber.

“Those aren’t the friendliest conditions,” he said. “You have to come up with creative solutions.”

The researchers succeeded and took video footage of ethane-methane rain and snow. The group also studied the freezing temperatures for methane and ethane lakes and determined that, because of a small amount of nitrogen in the liquid, the lakes freeze at lower temperatures than would be expected: 75 Kelvin, or -324 degrees Fahrenheit, instead of 90.5 Kelvin.

“That’s a big deal,” said Richardson. “That means you don’t have to worry about icebergs.”

The researchers are looking to continue the work with NASA to update the Titan Submarine design.

Publication: I.A. Richardson, et al., “Experimental PρT-x measurements of liquid methane-ethane-nitrogen mixtures,” Fluid Phase Equilibria, 2018; doi:10.1016/j.fluid.2018.01.023

Source: Jake Leachman, Washington State University

Sunlight glints off of Titan’s northern seas this near-infrared, color mosaic from NASA’s Cassini spacecraft. NASA/JPL/Univ. Arizona/Univ. Idaho (Featured Image Caption)