Do Exoplanet Scientists Have Favorite Exoplanets?

Artist rendition of the PSR B1257+12. (Credit: NASA/JPL-Caltech/R. Hurt)

Exoplanets have become quite the sensation over the last decade-plus, with scientists confirming new exoplanets on a regular basis thanks to NASA’s Kepler and TESS missions, along with the James Webb Space Telescope recently examining exoplanet atmospheres, as well. It’s because of these discoveries that exoplanet science has turned into an exciting field of intrigue and wonder, but do the very same scientists who study these wonderful and mysterious worlds have their own favorite exoplanets? As it turns out, four such exoplanet scientists, sometimes referred to as “exoplaneteers”, were kind enough to share their favorites with Universe Today!

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What if we’re truly alone?

Credit: Pixabay

At least once, you’ve looked up at the night sky and asked the same longstanding question we’ve all asked at least once, “Are we alone?” With all those points of light out there, we can’t be the only intelligent beings in the universe, right? There must be at least one technological civilization aside from us in the great vastness that we call the cosmos.

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Will Triton finally answer, ‘Are we alone?’

NASA’s Voyager 2 took this global color mosaic of Neptune’s largest moon, Triton, in 1989. (Credit: NASA/NASA-JPL/USGS)

We recently examined how and why Saturn’s icy moon, Enceladus, could answer the longstanding question: Are we alone? With its interior ocean and geysers of water ice that shoot out tens of kilometers into space that allegedly contains the ingredients for life, this small moon could be a prime target for future astrobiology missions. But Enceladus isn’t the only location in our solar system with active geysers, as another small moon near the edge of the solar system shares similar characteristics, as well. This is Neptune’s largest moon, Triton, which has been visited only once by NASA’s Voyager 2 in 1989. But are Triton’s geysers the only characteristics that make it a good target for astrobiology and finding life beyond Earth?

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Searching for Life on Highly Eccentric Exoplanets

Artist’s rendition of a hypothetical highly eccentric exoplanet (Credit: NASA/JPL-Caltech)

When we think about finding life beyond Earth, especially on exoplanets, we immediately want to search for the next Earth, or Earth 2.0. We want an exoplanet that orbits a star firmly in its habitable zone (HZ) with vast oceans of liquid water, and plenty of land to go around. An exoplanet like that most certainly has life, right? But what if we’re looking in the wrong places? What if we find life on exoplanets that don’t possess the aforementioned characteristics, i.e., Earth 2.0?

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Another Reason Red Dwarfs Might Be Bad for Life: No Asteroid Belts

In a recent study accepted to The Astrophysical Journal Letters, a team of researchers at the University of Nevada, Las Vegas (UNLV) investigated the potential for life on exoplanets orbiting M-dwarf stars, also known as red dwarfs, which are both smaller and cooler than our own Sun and is currently open for debate for their potential for life on their orbiting planetary bodies. The study examines how a lack of an asteroid belt might indicate a less likelihood for life on terrestrial worlds.

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Will Europa finally answer, ‘Are we alone?’

While NASA’s much-lauded Space Launch System stands ready for its maiden flight later this month with the goal of sending astronauts back to the Moon in the next few years, our gazes once again turn to the stars as we continue to ask the question that has plagued humankind since time immemorial: Are we alone? While there are several solar system locales that we can choose from to conduct our search for life beyond Earth, to include Mars and Saturn’s moons, Titan and Enceladus, one planetary body orbiting the largest planet in the solar system has peaked the interest of scientists since the 1970s.

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Mars Rovers Will Need to Dig Deeper If They Want to Find Evidence of Life

The search for life—even ancient life—on Mars is trickier than we thought. In a recent study published in the journal Astrobiology, researchers have determined that NASA’s Mars Perseverance (Percy) Rover will have to dig two meters (6.6 feet) beneath the Martian surface in order to find traces of ancient life. This is because the surface of Mars is constantly bombarded with extreme levels of solar radiation that scientists hypothesize would quickly degrade small molecules such as amino acids. The reason for this extreme level of radiation is due to the absence of a magnetic field, which scientists believe was stripped away billions of years ago when the planet’s liquid outer core ceased to produce the dynamo that created the field.

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Galactic Panspermia: Interstellar Dust Could Transport Life from Star to Star

A new study from the University of Edinburgh suggests that life could be distributed throughout the cosmos by interstellar dust. Credit: ESO/R. Fosbury (ST-ECF)

The theory of Panspermia states that life exists through the cosmos, and is distributed between planets, stars and even galaxies by asteroids, comets, meteors and planetoids. In this respect, life began on Earth about 4 billion years ago after microorganisms hitching a ride on space rocks landed on the surface. Over the years, considerable research has been devoted towards demonstrating that the various aspects of this theory work.

The latest comes from the University of Edinburgh, where Professor Arjun Berera offers another possible method for the transport of life-bearing molecules. According to his recent study, space dust that periodically comes into contact with Earth’s atmosphere could be what brought life to our world billions of years ago. If true, this same mechanism could be responsible for the distribution of life throughout the Universe.

For the sake of his study, which was recently published in Astrobiology under the title “Space Dust Collisions as a Planetary Escape Mechanism“, Prof. Berera examined the possibility that space dust could facilitate the escape of particles from Earth’s atmosphere. These include molecules that indicate the presence of life on Earth (aka. biosignatures), but also microbial life and molecules that are essential to life.

The theory of Panspermia states that life is distributed throughout the Universe by microbes traveling on objects between star system. Credit: NASA/Jenny Mottor

Fast-moving flows of interplanetary dust impact our atmosphere on a regular basis, at a rate of about 100,000 kg (110 tons) a day. This dust ranges in mass from 10-18 to 1 gram, and can reach speeds of 10 to 70 km/s (6.21 to 43.49 mps). As a result, this dust is capable of impacting Earth with enough energy to knock molecules out of the atmosphere and into space.

These molecules would consist largely of those that are present in the thermosphere. At this level, those particles would consist largely of chemically disassociated elements, such as molecular nitrogen and oxygen. But even at this high altitude, larger particles – such as those that are capable of harboring bacteria or organic molecules – have also been known to exist. As Dr. Berera states in his study:

“For particles that form the thermosphere or above or reach there from the ground, if they collide with this space dust, they can be displaced, altered in form or carried off by incoming space dust. This may have consequences for weather and wind, but most intriguing and the focus of this paper, is the possibility that such collisions can give particles in the atmosphere the necessary escape velocity and upward trajectory to escape Earth’s gravity.”

Of course, the process of molecules escaping our atmosphere presents certain difficulties. For starters, it requires that there be enough upward force that can accelerate these particles to escape velocity speeds. Second, if these particle are accelerated from too low an altitude (i.e. in the stratosphere or below), the atmospheric density will be high enough to create drag forces that will slow the upward-moving particles.

Photo of an aurora taken by astronaut Doug Wheelock from the International Space Station on July 25th, 2010. Credit: Image Science & Analysis Laboratory, NASA Johnson Space Center

In addition, as a result of their fast upward travel, these particle would undergo immense heating to the point of evaporation. So while wind, lighting, volcanoes, etc. would be capable of imparting huge forces at lower altitudes, they would not be able to accelerate intact particles to the point where they could achieve escape velocity. On the other hand, in the upper part of the mesosphere and thermosphere, particles would not suffer much drag or heating.

As such, Berera concludes that only atoms and molecules that are already found in the higher atmosphere could be propelled into space by space dust collisions. The mechanism for propelling them there would likely consist of a double state approach, whereby they are first hurled into the lower thermosphere or higher by some mechanism and then propelled even harder by fast space dust collision.

After calculating the speed at which space dust impacts our atmosphere, Berera determined that molecules that exist at an altitude of 150 km (93 mi) or higher above Earth’s surface would be knocked beyond the limit of Earth’s gravity. These molecules would then be in near-Earth space, where they could be picked up by passing objects such as comets, asteroid or other Near-Earth Objects (NEO) and carried to other planets.

Naturally, this raises another all-important question, which is whether or not these organisms could survive in space. But as Berera notes, previous studies have borne out the ability of microbes to survive in space:

“Should some microbial particles manage the perilous journey upward and out of the Earth’s gravity, the question remains how well they will survive in the harsh environment of space. Bacterial spores have been left on the exterior of the International Space Station at altitude ~400km, in a near vacuum environment of space, where there is nearly no water, considerable radiation, and with temperatures ranging from 332K on the sun side to 252K on the shadow side, and have survived 1.5 years.”

The tiny Tardigrade: Nature's toughest creature? (Image Credit: Katexic Publications, unaltered, CC2.0)
The tiny Tardigrade (aka. “water bear”), which could be the toughest creature on Earth. Credit: Katexic Publications, unaltered, CC2.0)

Another thing Berera considers is the strange case of tardigrades, the eight-legged micro-animals that are also known as “water bears”. Previous experiments have shown that this species is capable of surviving in space, being both strongly resistant to radiation and desiccation. So it is possible that such organisms, if they were knocked out of Earth’s upper atmosphere, could survive long enough to hitch a ride to another planet

In the end, these finding suggests that large asteroid impacts may not be the only mechanism responsible for life being transferred between planets, which is what proponents of Panspermia previously thought. As Berera stated in a University of Edinburgh press statement:

“The proposition that space dust collisions could propel organisms over enormous distances between planets raises some exciting prospects of how life and the atmospheres of planets originated. The streaming of fast space dust is found throughout planetary systems and could be a common factor in proliferating life.”

In addition to offering a fresh take on Panspermia, Berera’s study is also significant when it comes to the study of how life evolved on Earth. If biological molecules and bacteria have been escaping Earth’s atmosphere continuously over the course of its existence, then this would suggest that it could still be floating out in the Solar System, possibly within comets and asteroids.

These biological samples, if they could be accessed and studied, would serve as a timeline for the evolution of microbial life on Earth. It’s also possible that Earth-borne bacteria survive today on other planets, possibly on Mars or other bodies where they locked away in permafrost or ice. These colonies would basically be time capsules, containing preserved life that could date back billions of years.

Further Reading: University of Edinburgh, Astrobiology

What Did Cassini Teach Us?

What Did Cassini Teach Us?
What Did Cassini Teach Us?


Ask me my favorite object in the Solar System, especially to see through a telescope, and my answer is always the same: Saturn.

Saturn is this crazy, ringed world, different than any other place we’ve ever seen. And in a small telescope, you can really see the ball of the planet, you can see its rings. It’s one thing to see a world like this from afar, a tiny jumping image in a telescope. To really appreciate and understand a place like Saturn, you’ve got to visit.

And thanks to NASA’s Cassini spacecraft, that’s just what we’ve been doing for the last 13 years. Take a good close look at this amazing ringed planet and its moons, and studying it from every angle.

Space Probes
Cassini orbiting Saturn. Credit: NASA

Throughout this article, I’m going to regale you with the amazing discoveries made by Cassini at Saturn. What it taught us, and what new mysteries it uncovered.

NASA’s Cassini spacecraft was launched from Earth on October 15, 1997. Instead of taking the direct route, it made multiple flybys of Venus, a flyby of Earth and a flyby of Jupiter. Each one of these close encounters boosted Cassini’s velocity, allowing it to make the journey with less escape velocity from Earth.

It arrived at Saturn on July 1st, 2004 and began its science operations shortly after that. The primary mission lasted 4 years, and then NASA extended its mission two more times. The first ending in 2010, and the second due to end in 2017. But more on that later.

Before Cassini, we only had flybys of Saturn. NASA’s Pioneer 11, and Voyagers 1 and 2 both zipped past the planet and its moons, snapping pictures as they went.

But Cassini was here to stay. To orbit around and around the planet, taking photos, measuring magnetic fields, and studying chemicals.

For Saturn itself, Cassini was able to make regular observations of the planet as it passed through entire seasons. This allowed it to watch how the weather and atmospheric patterns changed over time. The spacecraft watched lightning storms dance through the cloudtops at night.

This series of images from NASA’s Cassini spacecraft shows the development of the largest storm seen on the planet since 1990. These true-color and composite near-true-color views chronicle the storm from its start in late 2010 through mid-2011, showing how the distinct head of the storm quickly grew large but eventually became engulfed by the storm’s tail. Credit: NASA/JPL-Caltech/Space Science Institute

Two highlights. In 2010, Cassini watched a huge storm erupt in the planet’s northern hemisphere. This storm dug deep into Saturn’s lower atmosphere, dredging up ice from a layer 160 kilometers below and mixing it onto the surface. This was the first time that astronomers were able to directly study this water ice on Saturn, which is normally in a layer hidden from view.

Natural color images taken by NASA’s Cassini wide-angle camera, showing the changing appearance of Saturn’s north polar region between 2012 and 2016.. Credit: NASA/JPL-Caltech/Space Science Institute/Hampton University

The second highlight, of course, is the massive hexagonal storm churning away in Saturn’s northern pole. This storm was originally seen by Voyager, but Cassini brought its infrared and visible wavelength instruments to bear.

Why a hexagon? That’s still a little unclear, but it seems like when you rotate fluids of different speeds, you get multi-sided structures like this.

Cassini showed how the hexagonal storm has changed in color as Saturn moved through its seasons.

This is one of my favorite images sent back by Cassini. It’s the polar vortex at the heart of the hexagon. Just look at those swirling clouds.

The polar vortex, in all its glory. Credit: NASA/JPL-Caltech/Space Science Institute

Now, images of Saturn itself are great and all, but there was so much else for Cassini to discover in the region.

Cassini studied Saturn’s rings in great detail, confirming that they’re made up of ice particles, ranging in size as small a piece of dust to as large as a mountain. But the rings themselves are actually quite thin. Just 10 meters thick in some places. Not 10 kilometers, not 10 million kilometers, 10 meters, 30 feet.

The spacecraft helped scientists uncover the source of Saturn’s E-ring, which is made up of fresh icy particles blasting out of its moon Enceladus. More on that in a second too.

Vertical structures, among the tallest seen in Saturn’s main rings, rise abruptly from the edge of Saturn’s B ring to cast long shadows on the ring in this image taken by NASA’s Cassini spacecraft two weeks before the planet’s August 2009 equinox. Credit: NASA/JPL/Space Science Institute

Here’s another one of my favorite images of the mission. You’re looking at strange structures in Saturn’s B-ring. Towering pillars of ring material that rise 3.5 kilometers above the surrounding area and cast long shadows. What is going on here?

They’re waves, generated in the rings and enhanced by nearby moons. They move and change over time in ways we’ve never been able to study anywhere else in the Solar System.

Daphnis, one of Saturn’s ring-embedded moons, is featured in this view, kicking up waves as it orbits within the Keeler gap. Credit: NASA/JPL-Caltech/Space Science Institute

Cassini has showed us that Saturn’s rings are a much more dynamic place than we ever thought. Some moons are creating rings, other moons are absorbing or distorting them. The rings generate bizarre spoke patterns larger than Earth that come and go because of electrostatic charges.

Speaking of moons, I’m getting to the best part. What did Cassini find at Saturn’s moons?

Let’s start with Titan, Saturn’s largest moon. Before Cassini, we only had a few low resolution images of this fascinating world. We knew Titan had a dense atmosphere, filled with nitrogen, but little else.

Cassini was carrying a special payload to assist with its exploration of Titan: the Huygens lander. This tiny probe detached from Cassini just before its arrival at Saturn, and parachuted through the cloudtops on January 14, 2005, analyzing all the way. Huygens returned images of its descent through the atmosphere, and even images of the freezing surface of Titan.

Huygen’s view of Titan. Credit: ESA/NASA/JPL/University of Arizona

But Cassini’s own observations of Titan took the story even further. Instead of a cold, dead world, Cassini showed that it has active weather, as well as lakes, oceans and rivers of hydrocarbons. It has shifting dunes of pulverized rock hard water ice.

If there’s one place that needs exploring even further, it’s Titan. We should return with sailboats, submarines and rovers to better explore this amazing place.

A view of Mimas from the Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

We learned, without a shadow of a doubt, that Mimas absolutely looks like the Death Star. No question. But instead of a megalaser, this moon has a crater a third of its own size.

Saturn’s moon Iapetus. Image credit: NASA/JPL/SSI

Cassini helped scientists understand why Saturn’s moon Iapetus has one light side and one dark side. The moon is tidally locked to Saturn, its dark side always leading the moon in orbit. It’s collecting debris from another Saturnian moon, Phoebe, like bugs hitting the windshield of a car.

Perhaps the most exciting discovery that Cassini made during its mission is the strange behavior of Saturn’s moon Enceladus. The spacecraft discovered that there are jets of water ice blasting out of the moon’s southern pole. An ocean of liquid water, heated up by tidal interactions with Saturn, is spewing out into space.

And as you know, wherever we find water on Earth, we find life. We thought that water in the icy outer Solar System would be hard to reach, but here it is, right at the surface, venting into space, and waiting for us to come back and investigate it further.

Icy water vapor geysers erupting from fissures on Enceladus. Credit: NASA/JPL

On September 15, 2017, the Cassini mission will end. How do we know it’s going to happen on this exact date? Because NASA is going to crash the spacecraft into Saturn, killing it dead.

That seems a little harsh, doesn’t it, especially for a spacecraft which has delivered so many amazing images to us over nearly two decades of space exploration? And as we’ve seen from NASA’s Opportunity rover, still going, 13 years longer than anticipated. Or the Voyagers, out in the depths of the void, helping us explore the boundary between the Solar System and interstellar space. These things are built to last.

The problem is that the Saturnian system contains some of the best environments for life in the Solar System. Saturn’s moon Enceladus, for example, has geysers of water blasting out into space.

Cassini spacecraft is covered in Earth-based bacteria and other microscopic organisms that hitched a ride to Saturn, and would be glad to take a nice hot Enceladian bath. All they need is liquid water and a few organic chemicals to get going, and Enceladus seems to have both.

NASA feels that it’s safer to end Cassini now, when they can still control it, than to wait until they lose communication or run out of propellant in the future. The chances that Cassini will actually crash into an icy moon and infect it with our Earth life are remote, but why take the risk?
For the last few months, Cassini has been taking a series of orbits to prepare itself for its final mission. Starting in April, it’ll actually cross inside the orbit of the rings, getting closer and closer to Saturn. And on September 15th, it’ll briefly become a meteor, flashing through the upper atmosphere of Saturn, gone forever.

This graphic illustrates the Cassini spacecraft’s trajectory, or flight path, during the final two phases of its mission. The view is toward Saturn as seen from Earth. The 20 ring-grazing orbits are shown in gray; the 22 grand finale orbits are shown in blue. The final partial orbit is colored orange. Image credit: NASA/JPL-Caltech/Space Science Institute

Even in its final moments, Cassini is going to be sciencing as hard as it can. We’ll learn more about the density of consistency of the rings close to the planet. We’ll learn more about the planet’s upper atmosphere, storms and clouds with the closest possible photographs you can take.

And then it’ll all be over. The perfect finale to one of the most successful space missions in human history. A mission that revealed as many new mysteries about Saturn as it helped us answer. A mission that showed us not only a distant alien world, but our own planet in perspective in this vast Solar System. I can’t wait to go back.

How have the photos from Cassini impacted your love of astronomy? Let me know your thoughts in the comments.