Life Could Be Evolving Right Now On Nearest Exoplanets

Rocky, Earth-like planets orbiting our closest stars could host life, according to a new study that raises the excitement about exoplanets.

When rocky, Earth-like planets were discovered orbiting in the habitable zone of some of our closest stars, excitement skyrocketed — until hopes for life were dashed by the high levels of radiation bombarding those worlds.

Proxima-b, only 4.24 light years away, receives 250 times more X-ray radiation than Earth and could experience deadly levels of ultraviolet radiation on its surface. How could life survive such a bombardment? Cornell University astronomers say that life already has survived this kind of fierce radiation, and they have proof: you.

Lisa Kaltenegger and Jack O’Malley-James make their case in a new paper, published in Monthly Notices of the Royal Astronomical Society. Kaltenegger is associate professor of astronomy and director of Cornell’s Carl Sagan Institute, at which O’Malley-James is a research associate.

All of life on Earth today evolved from creatures that thrived during an even greater UV radiation assault than Proxima-b, and other nearby exoplanets, currently endure. The Earth of 4 billion years ago was a chaotic, irradiated, hot mess. Yet in spite of this, life somehow gained a toehold and then expanded.

The same thing could be happening at this very moment on some of the nearest exoplanets, according to Kaltenegger and O’Malley-James. The researchers modeled the surface UV environments of the four exoplanets closest to Earth that are potentially habitable: Proxima-b, TRAPPIST-1e, Ross-128b and LHS-1140b.

These planets orbit small red dwarf stars which, unlike our sun, flare frequently, bathing their planets in high-energy UV radiation. While it is unknown exactly what conditions prevail upon the surface of the planets orbiting these flaring stars, it is known that such flares are biologically damaging and can cause erosion in planetary atmospheres. High levels of radiation cause biological molecules like nucleic acids to mutate or even shut down.

O’Malley-James and Kaltenegger modeled various atmospheric compositions, from ones similar to present-day Earth to “eroded” and “anoxic” atmospheres — those with very thin atmospheres that don’t block UV radiation well and those without the protection of ozone, respectively. The models show that as atmospheres thin and ozone levels decrease, more high-energy UV radiation reaches the ground. The researchers compared the models to Earth’s history, from nearly 4 billion years ago to today.

Although the modeled planets receive higher UV radiation than that emitted by our own sun today, this is significantly lower than what Earth received 3.9 billion years ago.

“Given that the early Earth was inhabited,” the researchers wrote, “we show that UV radiation should not be a limiting factor for the habitability of planets orbiting M stars. Our closest neighboring worlds remain intriguing targets for the search for life beyond our solar system.”

BREAKING NEWS: Scientists Set to Unveil First Picture of a Black Hole

On Wednesday, astronomers across the globe will hold “six major press conferences” simultaneously to announce the first results of the Event Horizon Telescope (EHT), which was designed precisely for that purpose.

Of all the forces or objects in the Universe that we cannot see – including dark energy and dark matter – none has frustrated human curiosity so much as the invisible digestive system that swallow stars like so many specks of dust.

“More than 50 years ago, scientists saw that there was something very bright at the center of our galaxy,” says Paul McNamara, an astrophysicist at the European Space Agency and an expert on black holes.

“It has a gravitational pull strong enough to make stars orbit around it very quickly – as fast as 20 years.”

To put that in perspective, our Solar System takes about 230 million years to circle the center of the Milky Way.

Eventually, astronomers speculated that these bright spots were in fact “black holes” – a term coined by American physicist John Archibald Wheeler in the mid-1960s – surrounded by a swirling band of white-hot gas and plasma.

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Curiosity Captured Two Solar Eclipses on Mars

When NASA’s Curiosity Mars rover landed in 2012, it brought along eclipse glasses. The solar filters on its Mast Camera (Mastcam) allow it to stare directly at the Sun. Over the past few weeks, Curiosity has been putting them to good use by sending back some spectacular imagery of solar eclipses caused by Phobos and Deimos, Mars’ two moons.

Two Solar Eclipse Viewed From Mars Caused by Phobos and Deimos

Phobos, which is about 7 miles (11.5 kilometers) across, was imaged on March 26, 2019 (the 2,359th sol, or Martian day, of Curiosity’s mission); Deimos, which is about 1.5 miles (2.3 kilometers) across, was photographed on March 17, 2019 (Sol 2350). Phobos doesn’t completely cover the Sun, so it would be considered an annular eclipse. Because Deimos is so small compared to the disk of the Sun, scientists would say it’s transiting the Sun.

In addition to capturing each moon crossing in front of the Sun, one of Curiosity’s Navigation Cameras (Navcams) observed the shadow of Phobos on March 25, 2019 (Sol 2358). As the moon’s shadow passed over the rover during sunset, it momentarily darkened the light.

Solar eclipses have been seen many times by Curiosity and other rovers in the past. Besides being cool – who doesn’t love an eclipse? – these events also serve a scientific purpose, helping researchers fine-tune their understanding of each moon’s orbit around Mars.

Heavy Metal Planet Fragment Survives Destruction From Dead Star

A fragment of a planet that has survived the death of its star has been discovered by University of Warwick astronomers in a disc of debris formed from destroyed planets, which the star ultimately consumes.

The iron and nickel rich planetesimal survived a system-wide cataclysm that followed the death of its host star, SDSS J122859.93+104032.9. Believed to have once been part of a larger planet, its survival is all the more astonishing as it orbits closer to its star than previously thought possible, going around it once every two hours.

The discovery, reported in the journal Science, is the first time that scientists have used spectroscopy to discover a solid body in orbit around a white dwarf, using subtle variations in the emitted light to identify additional gas that the planetesimal is generating.

Using the Gran Telescopio Canarias in La Palma, the scientists studied a debris disc orbiting a white dwarf 410 light years away, formed by the disruption of rocky bodies composed of elements such as iron, magnesium, silicon, and oxygen — the four key building blocks of the Earth and most rocky bodies. Within that disc they discovered a ring of gas streaming from a solid body, like a comet’s tail. This gas could either be generated by the body itself or by evaporating dust as it collides with small debris within the disc.

The astronomers estimate that this body has to be at least a kilometre in size, but could be as large as a few hundred kilometres in diameter, comparable to the largest asteroids known in our Solar System.

White dwarfs are the remains of stars like our sun that have burnt all their fuel and shed their outer layers, leaving behind a dense core which slowly cools over time. This particular star has shrunk so dramatically that the planetesimal orbits within its sun’s original radius. Evidence suggests that it was once part of a larger body further out in its solar system and is likely to have been a planet torn apart as the star began its cooling process.

Lead author Dr Christopher Manser, a Research Fellow in the Department of Physics, said: “The star would have originally been about two solar masses, but now the white dwarf is only 70% of the mass of our Sun. It is also very small — roughly the size of the Earth — and this makes the star, and in general all white dwarfs, extremely dense.

“The white dwarf’s gravity is so strong — about 100,000 times that of the Earth’s — that a typical asteroid will be ripped apart by gravitational forces if it passes too close to the white dwarf.”

Professor Boris Gaensicke, co-author from the Department of Physics, adds: “The planetesimal we have discovered is deep into the gravitational well of the white dwarf, much closer to it than we would expect to find anything still alive. That is only possible because it must be very dense and/or very likely to have internal strength that holds it together, so we propose that it is composed largely of iron and nickel.

“If it was pure iron it could survive where it lives now, but equally it could be a body that is rich in iron but with internal strength to hold it together, which is consistent with the planetesimal being a fairly massive fragment of a planet core. If correct, the original body was at least hundreds of kilometres in diameter because it is only at that point planets begin to differentiate — like oil on water — and have heavier elements sink to form a metallic core.”

The discovery offers a hint as to what planets may reside in other solar systems, and a glimpse into the future of our own.

Dr Christopher Manser said: “As stars age they grow into red giants, which ‘clean out’ much of the inner part of their planetary system. In our Solar System, the Sun will expand up to where the Earth currently orbits, and will wipe out Earth, Mercury, and Venus. Mars and beyond will survive and will move further out.

“The general consensus is that 5-6 billion years from now, our Solar System will be a white dwarf in place of the Sun, orbited by Mars, Jupiter, Saturn, the outer planets, as well as asteroids and comets. Gravitational interactions are likely to happen in such remnants of planetary systems, meaning the bigger planets can easily nudge the smaller bodies onto an orbit that takes them close to the white dwarf, where they get shredded by its enormous gravity.

“Learning about the masses of asteroids, or planetary fragments that can reach a white dwarf can tell us something about the planets that we know must be further out in this system, but we currently have no way to detect.

“Our discovery is only the second solid planetesimal found in a tight orbit around a white dwarf, with the previous one found because debris passing in front of the star blocked some of its light — that is the “transit method” widely used to discover exoplanets around Sun-like stars. To find such transits, the geometry under which we view them has to be very finely tuned, which means that each system observed for several hours mostly leads to nothing. The spectroscopic method we developed in this research can detect close-in planetesimals without the need for a specific alignment. We already know of several other systems with debris discs very similar to SDSS J122859.93+104032.9, which we will study next. We are confident that we will discover additional planetesimals orbiting white dwarfs, which will then allow us to learn more about their general properties.”

Dark Matter Is Not Made Up Of Tiny Black Holes

An international team of researchers has put a theory speculated by the late Stephen Hawking to its most rigorous test to date, and their results have ruled out the possibility that primordial black holes smaller than a tenth of a millimeter make up most of dark matter. Details of their study have been published in this week’s Nature Astronomy.

Scientists know that 85 per cent of the matter in the Universe is made up of dark matter. Its gravitational force prevents stars in our Milky Way from flying apart. However, attempts to detect such dark matter particles using underground experiments, or accelerator experiments including the world’s largest accelerator, the Large Hadron Collider, have failed so far.

This has led scientists to consider Hawking’s 1974 theory of the existence of primordial black holes, born shortly after the Big Bang, and his speculation that they could make up a large fraction of the elusive dark matter scientists are trying to discover today.

An international team of researchers, led by Kavli Institute for the Physics and Mathematics of the Universe Principal Investigator Masahiro Takada, PhD candidate student Hiroko Niikura, Professor Naoki Yasuda, and including researchers from Japan, India and the US, have used the gravitational lensing effect to look for primordial black holes between Earth and the Andromeda galaxy. Gravitational lensing, an effect first suggested by Albert Einstein, manifests itself as the bending of light rays coming from a distant object such as a star due to the gravitational effect of an intervening massive object such as a primordial black hole. In extreme cases, such light bending causes the background star to appear much brighter than it originally is.

However, gravitational lensing effects are very rare events because it requires a star in the Andromeda galaxy, a primordial black hole acting as the gravitational lens, and an observer on Earth to be exactly in line with one another. So to maximize the chances of capturing an event, the researchers used the Hyper Suprime-Cam digital camera on the Subaru telescope in Hawaii, which can capture the whole image of the Andromeda galaxy in one shot. Taking into account how fast primordial black holes are expected to move in interstellar space, the team took multiple images to be able to catch the flicker of a star as it brightens for a period of a few minutes to hours due to gravitational lensing.

From 190 consecutive images of the Andromeda galaxy taken over seven hours during one clear night, the team scoured the data for potential gravitational lensing events. If dark matter consists of primordial black holes of a given mass, in this case masses lighter than the moon, the researchers expected to find about 1000 events. But after careful analyses, they could only identify one case. The team’s results showed primordial black holes can contribute no more than 0.1 per cent of all dark matter mass. Therefore, it is unlikely the theory is true.

The researchers are now planning to further develop their analysis of the Andromeda galaxy. One new theory they will investigate is to find whether binary black holes discovered by gravitational wave detector LIGO are in fact primordial black holes.

Calculating Temperature Inside Moon To Help Reveal Its Inner Structure

Little is known about the inner structure of the Moon, but a major step forward was made by a University of Rhode Island scientist who conducted experiments that enabled her to determine the temperature at the boundary of the Moon’s core and mantle.

She found the temperature to be between 1,300 and 1,470 degrees Celsius, which is at the high end of an 800 degree range that previous scientists had determined.

“In order to understand the interior structure of the Moon today, we needed to nail down the thermal state better,” said Ananya Mallik, a URI assistant professor of geosciences who joined the University faculty in December 2018. “Now we have the two anchor points — the core-mantle boundary and the surface temperature measured by Apollo — and that will help us create a temperature profile through the Moon. We need that temperature profile to determine the internal state, structure and composition of the Moon.”

The surface temperature of the Moon is approximately -20 C.

According to Mallik, the Moon has an iron core, like that of Earth, and previous research using seismic data had found that between 5 and 30 percent of the material at the boundary of the core and mantle was in a liquid or molten state.

“The big question is, why would we have some melt present in the Moon at that depth,” Mallik said.

To begin to answer this question, Mallik conducted a series of experiments in 2016 at the Bavarian Research Institute of Experimental Geochemistry and Geophysics in Germany using a multi-anvil device that can exert the high pressures found deep inside the Moon. She prepared a tiny sample of material similar to that found on the Moon, squeezed it in the device at 45,000 times the Earth’s atmospheric pressure, which is the pressure believed to exist at the Moon’s core-mantle boundary, and used a graphite heater to raise the temperature of the sample until it partially melted.

“The goal was to determine what temperature range would produce a 5 to 30 percent melt, which would tell us the temperature range of the core-mantle boundary,” she said.

Now that the temperature range at the boundary has been narrowed, scientists can begin to develop a more precise temperature profile of the Moon and proceed to determine a profile of the minerals that make up the mantle from its crust to its core.

“It’s important that we know the composition of the Moon to better understand why it has evolved as it has,” Mallik said. “The histories of the Earth and Moon have been intertwined since the beginning. In fact, both are the product of a great collision between proto-Earth and an approximately Mars-sized body that occurred over 4.5 billion years ago. So to understand our Earth better, we have to know our nearest neighbor because we all had a common start.

“Earth is complicated,” she continued. “Any similarity in the composition between Earth and the Moon can give us insight into how these two planetary bodies were formed, what were the energetics of the collision, and how elements were partitioned between them.”

The URI geoscientist noted that Earth has evolved through the process of plate tectonics, which is responsible for the distribution of the continents, the topography of Earth’s surface, the regulation of long-term climate, and perhaps even the origin of life. But there is no evidence of plate tectonics on the Moon.

“Everything on Earth happens because of plate tectonics,” she said. “What does this tell us about our own planet when the Moon doesn’t experience this process? It’s the same argument for why we study Mars and Venus. They are our next closest neighbors, and we all had a common start, but why are they so different from our planet?”

The next steps in Mallik’s research will involve experimentally determining the density of the molten material at the core-mantle boundary, which will further refine the temperature range. In collaboration with Heidi Fuqua Haviland at NASA’s Marshall Space Flight Center and Paul Bremner at the University of Florida, she will then combine these results with computational methods to derive the temperature profile and composition of the interior of the Moon.

Van Allen Probes Prepare for Final Descent into Earth’s Atmosphere

Two tough, resilient NASA spacecraft have been orbiting Earth for the past six and a half years, flying repeatedly through a hazardous zone of charged particles known as the Van Allen radiation belts. The twin Van Allen Probes have confirmed scientific theories and revealed new structures, compositions, and processes at work in these dynamic regions.

In February, the Van Allen Probes mission operations team at the Johns Hopkins Applied Physics Laboratory—where the probes were designed and built—began a series of orbit descent maneuvers that will position the satellites for an eventual re-entry into Earth’s atmosphere in approximately 15 years.

“At the new altitude, aerodynamic drag will bring down the satellites and eventually burn them up in the upper atmosphere,” said Nelli Mosavi, project manager for the Van Allen Probes at APL. “Our mission is to obtain great science data and also to ensure that we prevent more space debris so the next generations have the opportunity to explore space as well.”

Originally designated as a two-year mission because no one believed that a spacecraft could survive longer in the harsh radiation belts that surround Earth, these rugged spacecraft have operated without incident since 2012 and continue to enable groundbreaking discoveries about the Van Allen belts.

“The spacecraft and instruments have given us incredible insight into spacecraft operations in a high-radiation environment,” Mosavi said. “Everyone on the mission feels a real sense of pride and accomplishment in the work we’ve done and the science we’ve provided to the world—even as we begin the de-orbiting maneuvers.”

“We know that other planets in our solar system with magnetic fields have radiation belts,” said Sasha Ukhorskiy, a project scientist at APL. “We can assume that other bodies throughout the universe do too. By studying the belts and the physics associated with them here at Earth, and using our world as a natural laboratory, we can learn about how these structures function around other objects in the universe with magnetic fields.”

The magnetic field surrounding Earth creates a bubble known as the magnetosphere, which protects the planet from plasma blasts sent out by the sun. But it also serves to capture particles and can eventually settle these high-energy particle populations into radiation belts around Earth.

A complex chain of processes occurs in this near-Earth environment, acting like a giant particle accelerator and speeding some particles up to nearly the speed of light—more than 670 million miles an hour. These highly energized particles in the radiation belts can pose a number of hazards to space operations, as they can damage sensitive electronics.

During solar storms, conditions worsen, and the belts can swell in size, threatening nearby spacecraft.

“Our magnetic field does a pretty good job of shielding us from these solar blasts,” said David Sibeck, a mission scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “But some of their energy penetrates deep into the Earth’s field and, through a variety of mechanisms, powers up the radiation belts. When that happens, spacecraft in the belts had better look out: Trouble lies ahead in the form of short circuits, disrupted computer memory, and instrument failure.”
The Van Allen Probes were designed and built to be resilient in this extreme environment—and even their builders were surprised by their ability to withstand such harsh conditions.

“Over the past six and a half years, the Van Allen Probes have completed three full circuits around the magnetosphere, and measured more than 100 geomagnetic storms,” Ukhorskiy said. “The Van Allen Probes verified and quantified previously suggested theories, discovered new mechanisms that can sculpt near-Earth energetic particle populations, and used uniquely capable instruments to unveil unexpected features that were all but invisible to previous sensors.”

The information on particles and waves delivered by the Van Allen Probes has proved to be a treasure trove for space physics research. Findings and observations include multiple belt structures, including a third belt observed shortly after launch; definitive answers about particle acceleration processes; and the discovery of a nearly impenetrable barrier region that prevents the fastest and most energetic electrons from reaching Earth.