What Is A Super Earth?

The Universe is always surprising us with how little we know about… the Universe. It’s continuously presenting us with stuff we never imagined, or even thought possible. The search for extrasolar planets is a great example.

Since we started, astronomers have turned up over a thousand of them. These planets can be gigantic worlds with many times the mass of Jupiter, all the way down to little tiny planets smaller than Mercury. Astronomers are also finding one type of world that feels both familiar and yet totally alien… the super earth.

In the strictest sense, a super earth is just a planet with more mass than Earth, but less than a larger planet like Uranus or Neptune. So, you could have super earths made of rock and metal, or even ice and gas. These planets could have oceans and atmospheres, or made of nothing but hydrogen and helium. The goal, of course, is to find a rocky super earth located in the habitable zone. This is the region where the planets are the right distance from the star for liquid water to be present.

The first discovery of a potentially habitable super earth was in the star system Gliese 581.
Here, astronomers found 2 planets orbiting within the habitable zone. Gliese 581 c has a mass of 5 times the Earth, and orbits on the overly warm side of the habitable zone and, Gliese 581 d is 7.7 times the mass of the Earth, and is on the cold side of the zone.

We’ve now found dozens of super earths. One recent discovery, Kepler 11-b, has only 4 times the mass of the our planet and just 1.5 times its size.

You’re probably wondering about the gravity. The exact gravity depends on the ratio of the planet’s size to its mass. If you could stand on the surface of a super earth, you’d probably feel a higher gravity. Considering these planets can have 5 or more times the mass of Earth. But less gravity than you’d expect.

An increase in size makes a big difference. For example, if you could stand on the surface of Kepler 11-b, which is about 1.5 times bigger but a whopping 4 times more massive, you’d feel only 1.4 times the pull of Earth’s gravity.

Artist's impression of the trio of super earths.  Image credit: ESO
Artist’s impression of the trio of super earths. Image credit: ESO

Here’s the big question. Could a super earth support life?

Aquatic life would be no problem. Once you’re in the ocean, the effects of gravity are balanced out by the buoyancy of water. How well life could survive on land and in the air depends on the gravity of the world. With higher gravity, plants and animals wouldn’t be able to grow as tall. Animals would need thicker legs to support their weight. If the atmosphere was denser, likely because of the higher gravity, flying creatures could move more slowly with larger wingspans.

If intelligent life does develop on a heavy gravity world, it will have a much harder time getting into space. Reaching orbital velocity is already tremendously difficult from Earth. Just imagine how much more difficult it would be to launch rockets if everything was twice as heavy.

So, a big thank you to the astronomers showing us that there are all kinds of crazy worlds out there.

I just wish they weren’t so far away.

Why Einstein Will Never Be Wrong

Einstein Lecturing

One of the benefits of being an astrophysicist is your weekly email from someone who claims to have “proven Einstein wrong”. These either contain no mathematical equations and use phrases such as “it is obvious that..”, or they are page after page of complex equations with dozens of scientific terms used in non-traditional ways. They all get deleted pretty quickly, not because astrophysicists are too indoctrinated in established theories, but because none of them acknowledge how theories get replaced.

For example, in the late 1700s there was a theory of heat known as caloric. The basic idea of caloric was that it was a fluid that existed within materials. This fluid was self-repellant, meaning it would try to spread out as evenly as possible. We couldn’t observe this fluid directly, but the more caloric a material has the greater its temperature.

Ice-calorimeter
Ice-calorimeter from Antoine Lavoisier’s 1789 Elements of Chemistry. (Public Domain)

From this theory you get several predictions that actually work. Since you can’t create or destroy caloric, heat (energy) is conserved. If you put a cold object next to a hot object, the caloric in the hot object will spread out to the cold object until they reach the same temperature.  When air expands, the caloric is spread out more thinly, thus the temperature drops. When air is compressed there is more caloric per volume, and the temperature rises.

We now know there is no “heat fluid” known as caloric. Heat is a property of the motion (kinetic energy) of atoms or molecules in a material. So in physics we’ve dropped the caloric model in terms of kinetic theory. You could say we now know that the caloric model is completely wrong.

Except it isn’t. At least no more wrong than it ever was.

The basic assumption of a “heat fluid” doesn’t match reality, but the model makes predictions that are correct. In fact the caloric model works as well today as it did in the late 1700s. We don’t use it anymore because we have newer models that work better. Kinetic theory makes all the predictions caloric does and more. Kinetic theory even explains how the thermal energy of a material can be approximated as a fluid.

This is a key aspect of scientific theories. If you want to replace a robust scientific theory with a new one, the new theory must be able to do more than the old one. When you replace the old theory you now understand the limits of that theory and how to move beyond it.

In some cases even when an old theory is supplanted we continue to use it. Such an example can be seen in Newton’s law of gravity. When Newton proposed his theory of universal gravity in the 1600s, he described gravity as a force of attraction between all masses. This allowed for the correct prediction of the motion of the planets, the discovery of Neptune, the basic relation between a star’s mass and its temperature, and on and on. Newtonian gravity was and is a robust scientific theory.

Then in the early 1900s Einstein proposed a different model known as general relativity. The basic premise of this theory is that gravity is due to the curvature of space and time by masses.  Even though Einstein’s gravity model is radically different from Newton’s, the mathematics of the theory shows that Newton’s equations are approximate solutions to Einstein’s equations.  Everything Newton’s gravity predicts, Einstein’s does as well. But Einstein also allows us to correctly model black holes, the big bang, the precession of Mercury’s orbit, time dilation, and more, all of which have been experimentally validated.

So Einstein trumps Newton. But Einstein’s theory is much more difficult to work with than Newton’s, so often we just use Newton’s equations to calculate things. For example, the motion of satellites, or exoplanets. If we don’t need the precision of Einstein’s theory, we simply use Newton to get an answer that is “good enough.” We may have proven Newton’s theory “wrong”, but the theory is still as useful and accurate as it ever was.

Unfortunately, many budding Einsteins don’t understand this.

Binary waves from black holes. Image Credit: K. Thorne (Caltech) , T. Carnahan (NASA GSFC)
Binary waves from black holes. Image Credit: K. Thorne (Caltech) , T. Carnahan (NASA GSFC)

To begin with, Einstein’s gravity will never be proven wrong by a theory. It will be proven wrong by experimental evidence showing that the predictions of general relativity don’t work. Einstein’s theory didn’t supplant Newton’s until we had experimental evidence that agreed with Einstein and didn’t agree with Newton. So unless you have experimental evidence that clearly contradicts general relativity, claims of “disproving Einstein” will fall on deaf ears.

The other way to trump Einstein would be to develop a theory that clearly shows how Einstein’s theory is an approximation of your new theory, or how the experimental tests general relativity has passed are also passed by your theory.  Ideally, your new theory will also make new predictions that can be tested in a reasonable way.  If you can do that, and can present your ideas clearly, you will be listened to.  String theory and entropic gravity are examples of models that try to do just that.

But even if someone succeeds in creating a theory better than Einstein’s (and someone almost certainly will), Einstein’s theory will still be as valid as it ever was.  Einstein won’t have been proven wrong, we’ll simply understand the limits of his theory.

What Is The Big Rip?

Dr. Thad Szabo is a professor of physics and astronomy at Cerritos College. He’s also a regular contributor to many of our projects, like the Virtual Star Party and the Weekly Space Hangout. Thad has an encyclopedic knowledge of all things space, so we got him to explain a few fascinating concepts.

In this video, Thad explains the strange mystery of dark energy, and the even stranger idea of the Big Rip.

What is the ‘Big Rip?’

If we look at the expansion of the universe, at first it was thought that, as things are expanding while objects have mass, the mass is going to be attracted to other mass, and that should slow the expansion. Then, in the late 1990’s, you have the supernova surveys that are looking deeper into space than we’ve ever looked before, and measuring distances accurately to greater distances than we’ve ever seen before. Something really surprising came out, and that was what we’ll now use “dark energy” now to explain, and that is that the acceleration is not actually slowing down – it’s not even stopped. It’s actually getting faster, and if you look at the most distant objects, they’re actually moving away from us and the acceleration is increasing the acceleration of expansion. This is actually a huge result.

One of the ideas of trying to explain it is to use the “cosmological constant,” which is something that Einstein actually introduced to his field equations to try to keep the universe the same size. He didn’t like the idea of a universe changing, so he just kind of cooked up this term and threw it into the equations to say, alright, well if it isn’t supposed to expand or contract, if I make this little mathematical adjustment, it stays the same size.

Hubble comes along about ten years later, and is observing galaxies and measuring their red shifts and their distances, and says wait a minute – no the universe is expanding. And actually we should really credit that to Georges Lemaître, who was able to interpret Hubble’s data to come up with the idea of what we now call the Big Bang.

So, the expansion’s happening – wait, it’s getting faster. And now the attempt is to try to understand how dark energy works. Right now, most of the evidence points to this idea that the expansion will continue in the space between galaxies. That the forces of gravity, and especially magnetism and the strong nuclear force that holds protons and neutrons together in the center of an atom, would be strong enough that dark energy is never going to be able to pull those objects apart.

However, there’s a possibility that it doesn’t work like that. There’s actually a little bit of experimental evidence right now that, although it’s not well-established, that there’s a little bit of a bias with certain experiments that dark energy may get stronger over time. And, if it does so, the distances won’t matter – that any object will be pulled apart. So first, you will see all galaxies recede from each other, as space starts to grow bigger and bigger, faster and faster. Then the galaxies will start to be pulled apart. Then star systems, then planets from their stars, then stars themselves, and then other objects that would typically be held together by the much stronger forces, the electromagnetic force objects held by that will be pulled apart, and then eventually, nuclei in atoms.

So if dark energy behaves so that it gets stronger and stronger over time, it will eventually overcome everything, and you’ll have a universe with nothing left. That’s the ‘Big Rip’ – if dark energy gets stronger and stronger over time, it will eventually overcome any forces of attraction, and then everything is torn apart.

You can find more information from Dr. Thad Szabo at his YouTube channel.

Where Does Gravity Come From?

Gravity. The average person probably doesn’t think about it on a daily basis, but yet gravity affects our every move. Because of gravity, we fall down (not up), objects crash to the floor, and we don’t go flying off into space when we jump in the air. The old adage, “everything that goes up must come down” makes perfect sense to everyone because from the day we are born, we are seemingly bound to Earth’s surface due to this all-pervasive invisible force.

But physicists think about gravity all the time. To them, gravity is one of the mysteries to be solved in order to get a complete understanding of how the Universe works.

So, what is gravity and where does it come from?

To be honest, we’re not entirely sure.

Graphic courtesy University of Tennessee Knoxville.
Graphic courtesy University of Tennessee Knoxville.

We know from Isaac Newton and his law of gravitation that any two objects in the Universe exert a force of attraction on each other. This relationship is based on the mass of the two objects and the distance between them. The greater the mass of the two objects and the shorter the distance between them, the stronger the pull of the gravitational forces they exert on each other.

We also know that gravity can work in a complex system with several objects. For example, in our own Solar System, not only does the Sun exert gravity on all the planets, keeping them in their orbits, but each planet exerts a force of gravity on the Sun, as well as all the other planets, too, all to varying degrees based on the mass and distance between the bodies. And it goes beyond just our Solar System, as actually, every object that has mass in the Universe attracts every other object that has mass — again, all to varying degrees based on mass and distance.

A demonstration of gravity with balls on a rubber sheet. Credit: Stanford University.
A demonstration of gravity with balls on a rubber sheet. Credit: Stanford University.

With his theory of relativity, Albert Einstein explained how gravity is more than just a force: it is a curvature in the space-time continuum. That sounds like something straight out of science fiction, but simply put, the mass of an object causes the space around it to essentially bend and curve. This is often portrayed as a heavy ball sitting on a rubber sheet, and other smaller balls fall in towards the heavier object because the rubber sheet is warped from the heavy ball’s weight.

In reality, we can’t see curvature of space directly, but we can detect it in the motions of objects. Any object ‘caught’ in another celestial body’s gravity is affected because the space it is moving through is curved toward that object. It is similar to the way a coin would spiral down one of those penny slot cyclone machines you see at tourist shops, or the way bicycles spiral around a velodrome.

A 2-dimensional animation of how gravity works. Via NASA's Space Place..
A 2-dimensional animation of how gravity works. Via NASA’s Space Place..

We can also see the effects of gravity on light in a phenomenon called gravitational lensing. If an object in space is massive enough – such as a large galaxy or cluster of galaxies — it can cause an otherwise straight beam of light to curve around it, creating a lensing effect.

Images from the Hubble Space Telescope showing a gravitational lensing effect. Credit: NASA/ESA.
Images from the Hubble Space Telescope showing a gravitational lensing effect. Credit: NASA/ESA.

But these effects – where there are basically curves, hills and valleys in space — occur for reasons we can’t fully really explain. Besides being a characteristic of space, gravity is also a force (but it is the weakest of the four forces), and it might be a particle, too. Some scientists have proposed particles called gravitons cause objects to be attracted to one another. But gravitons have never actually been observed. Another idea is that gravitational waves are generated when an object is accelerated by an external force, but these waves have never been directly detected, either.

Our understanding of gravity breaks down at both the very small and the very big: at the level of atoms and molecules, gravity just stops working. And we can’t describe the insides of black holes and the moment of the Big Bang without the math completely falling apart.

The problem is that our understanding of both particle physics and the geometry of gravity is incomplete.

“Having gone from basically philosophical understandings of why things fall to mathematical descriptions of how things accelerate down inclines from Galileo, to Kepler’s equations describing planetary motion to Newton’s formulation of the Laws of Physics, to Einstein’s formulations of relativity, we’ve been building and building a more comprehensive view of gravity. But we’re still not complete,” said Dr. Pamela Gay. “We know that there still needs to be some way to unite quantum mechanics and gravity and actually be able to write down equations that describe the centers of black holes and the earliest moments of the Universe. But we’re not there yet.”

And so, the mystery remains … for now.

This “Minute Physics” video helps explain what we know about gravity:

We have written many articles about gravity for Universe Today. Here’s an article about gravity and antimatter, and here’s an article about the discovery of gravity. This recent article discusses how the latest research looks at quantum physics to explain gravity.

If you’d like more info on Gravity, check out The Constant Pull of Gravity: How Does It Work?, and here’s a link to Gravity on Earth Versus Gravity in Space: What’s the Difference?.

We’ve also recorded an entire episode of Astronomy Cast all about Gravity. Listen here, Episode 102: Gravity.

For further reading:
Cornell Astronomy
UT-Knoxville

Weekly Space Hangout – October 25, 2013: Preventing Asteroids, More Comets, Worldview Balloon

So much space news, so little time. We had a great Weekly Space Hangout with several of our familiar space journalist friends. No huge stories, but lots of interesting tidbits, about asteroid protection, balloon trips to the edge of space, and the discovery of the furthest galaxy.

Host: Fraser Cain

Panel: Alan Boyle, Amy Shira Teitel, David Dickinson, Nancy Atkinson, Elizabeth Howell

Stories:
Preventing Asteroid Strikes
Japanese Asteroid Cannon
How to see Other Comets
Furthest Galaxy Found
More than 1000 Exoplanets
Worldview Balloon Flights
Watch the Sun Split Apart
What’s the Weather on Titan
Spider Adapts to Return to Gravity
ExoMars Rover

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page.

NASA Astronaut Helped Actors Prepare for “Gravity”

Actors for a new movie coming out in October 2013 received tips about life in space from NASA astronaut Cady Coleman. “Gravity” is the story of two astronauts (played by George Clooney and Sandra Bullock) whose shuttle is destroyed by a run-in with space junk during an EVA, stranding them both in orbit and struggling for survival.

While developing her role, Bullock gave Coleman a call while she was aboard the space station. At the time, the actress asked Coleman to elaborate on what it’s like living and moving about in microgravity. “I told her that I had long hair, and if you pulled a hair out and pushed it against something, you could move yourself across the space station,” said Coleman. “That’s how little force it takes.”

You can see more of their discussion below, as well as the heart-pounding trailer for the movie:

NASA says that although this dire scenario makes for gripping Hollywood entertainment, NASA actively works to protect its astronauts and vehicles from the dangers portrayed in the movie. From protective shielding and meticulous and methodical training on the ground and in space covering everything from spacewalking to fires or decompression inside the space station, NASA’s ground crews and astronauts are as prepared as they can be for potential anomaly, no matter how remote they may be.

Read more about aspects of the International Space Station that you’ll see in the movie in this feature article from NASA.

A “Mini Jet” Juts from Saturn’s F Ring

We all know that Saturn’s moon Enceladus has a whole arsenal of geysers jetting a constant spray of ice out into orbit (and if you didn’t know, learn about it here) but Enceladus isn’t the only place in the Saturnian system where jets can be found — there are some miniature versions hiding out in the thin F ring as well!

Watch the 50-mile-wide Prometheus dip into the F ring (CLICK TO PLAY) NASA/JPL/SSI. Animation by J. Major.
Watch the 50-mile-wide Prometheus dip into the F ring (CLICK TO PLAY) NASA/JPL/SSI. Animation by J. Major.

The image above, captured by the Cassini spacecraft on June 20, 2013, shows a segment of the thin, ropy F ring that encircles Saturn just beyond the A ring (visible at upper right). The bright barb near the center is what scientists call a mini jet, thought to be caused by small objects getting dragged through the ring material as a result of repeated passings by the shepherd moon Prometheus.

Coincidentally, it’s gravitational perturbations by Prometheus that help form the objects — half-mile-wide snowball-like clusters of icy ring particles — in the first place.

Unlike the dramatic jets on Enceladus, which are powered by tidal stresses that flex the moon’s crust, these mini jets are much more subtle and occur at the casual rate of 4 mph (2 meters/second)… about the speed of a brisk walk.

The reflective jets themselves can be anywhere from 25 to 112 miles (40 to 180 kilometers) long.

See more images of mini jets — also called “classic trails” — below:

Various images of mini jets captured by Cassini from 2005 to 2008.
Various images of mini jets captured by Cassini from 2005 to 2008.

Over 500 of these features have been imaged by Cassini since 2005. Read more about mini jets here.

(And don’t worry, Enceladus… these little jets are interesting but they have nothing on you!)

Source: Cassini Imaging Central Laboratory for OPerationS (CICLOPS)

Image credits: NASA/JPL-Caltech/SSI/QMUL. 

The Scariest Part of “Gravity” is the Lack Thereof

I love science fiction films and I especially love it when the “science” part leans closer to fact than fiction. (Yes, I’m looking at you, Europa Report.) Now I’ve never seen an actual catastrophe in orbit (and I hope I never do) but I have to assume it’d look a whole lot like what’s happening in the upcoming film “Gravity,” opening in U.S. theaters on October 4. This full official trailer was released today.

A disaster film sure becomes a whole lot more interesting when everything is moving 18,000 miles an hour and there’s no up or down. And, of course, space. (!!!)

So what do you think? Will you be seeing Gravity? Share your thoughts in the comments…
Continue reading “The Scariest Part of “Gravity” is the Lack Thereof”

The New Trailer for “Gravity” Depicts a Dizzying Disaster… in Orbit!

If you’ve ever been involved in one, you know that even a minor vehicle accident is a confusing and scary event. Trying to desperately regain control of your own movement as you’re suddenly subjected to forces beyond your control is stressful and terrifying… now imagine it happening at 17,500 mph and 230 miles up and you’ve got an idea of what the upcoming film “Gravity” is about.

Still can’t quite picture it? Check out the latest trailer below:

Directed and written by Alfonso Cuarón and co-written with his son Jonas, “Gravity” is the story of two astronauts (played by George Clooney and Sandra Bullock) whose shuttle is destroyed by a run-in with space junk during an EVA, stranding them both in orbit.

If that wasn’t bad enough, their oxygen is running out and they have lost communication with the ground. Cast adrift in orbit, they have to figure out how to survive and get back home.

It’s like “Open Water” in space. Without the sharks. (Let’s hope things turn out better for them!)

I enjoy sci-fi and I especially enjoy when they try to get the “sci” part right. How do things move in microgravity? (Hint: really fast.) What happens when stuff smashes together? What would happen to the human body in that situation? And, most importantly for any movie, how do the people involved handle the experience?

Above all, “Gravity” is still a movie so it has to take us on a two-hour, candy-munching, soda-slurping ride. Based on this latest trailer, I’m confident that they’ve done their homework on the mechanics of movement in orbit… now let’s see if Cuarón (Children of Men, Y Tu Mamá También, Harry Potter and the Prisoner of Azkaban)  has once again worked his storytelling magic to bring the characters to free-falling life.

A Warner Bros. Pictures production, “Gravity” will be released in IMAX 3D and 2D this October. See the official movie site here.

ADDED 7/25: Here’s a new clip, titled “I’ve Got You”:

Video ©2013 Warner Bros. Entertainment. All rights reserved.

Hang On! Trailer for “Gravity” Previews Spacewalk Disaster Film

Yikes! The trailer for an upcoming film “Gravity” is absolutely terrifying. This movie won’t hit theaters until October 4, 2013, so we can expect to see more trailers after this first ‘teaser.” We do know it is directed by Alfonso Cuarón and stars Sandra Bullock and George Clooney. But with an emergency spacewalk likely taking place tomorrow at the International Space Station, the timing of the release of this trailer is just a bit eerie.

Bullock plays a medical engineer on her first shuttle mission, with veteran astronaut Matt Kowalsky (Clooney) in command of his last flight before retiring. But on a seemingly routine spacewalk, disaster strikes. The shuttle is destroyed, the space station is damaged, leaving the two astronauts completely alone and tethered to nothing but each other and spiraling out into the blackness.

Watch the teaser below:

The word on the street is that NASA was not consulted at all for this film, so we can only hope for a hint of reality (i.e., let hope it’s not another “Armageddon.”) But from the trailer, it seems to follow the recipe for any space disaster film: go into space, have the mission go awry, bring in the heroes to save the day. Guesses on thumbs up or down?