Posted on by Fraser Cain

Super Earths

An artist’s impression of Gliese 581d, an exoplanet about 20.3 light-years away from Earth, in the constellation Libra. Credit: NASA

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The holy grail in the search for extrasolar planets will be the discovery of Earthlike planets orbiting other stars. With better telescopes and techniques, astronomers will eventually be able to even detect the atmospheres of extrasolar planets and determine if there’s life there. Although Earth-sized planets are impossible to detect with current observatories, astronomers are now finding super earths.

A super Earth is a terrestrial planet orbiting a distant star. But instead of having the mass of our own planet, it might have 2, 5, or even 10 times the mass of the Earth. Although that makes them large, very massive planets, they’re not as large or massive as gas giants.

And just because they’re called super Earths doesn’t mean they’re habitable, or even Earthlike in climate at all. Super Earths could be orbiting close to their parent star, or well outside the solar system’s habitable zone.

Scientists haven’t completely settled on a definition for super Earths. Some believe a planet should be considered a super Earth if it’s a terrestrial planet between 1 and 10 Earth masses, while others think it should be between 5 and 10 Earth masses.

The first super Earth ever discovered was found in 1991 orbiting a pulsar. Obviously that wouldn’t really be a very habitable place to live. The first super earth found orbiting a main sequence star was found in 2005, orbiting the star Gliese 876. It’s estimated to have 7.5 times the mass of the Earth, and orbits its parent star every 2 days. With such a short orbital period, you can expect that it’s orbiting very close to its parent star. Temperatures on the surface of the planet reach 650 kelvin.

The first super earth found within its star’ habitable zone was Gliese 581 c. It’s estimated to have 5 Earth masses, and orbits its parent star at a distance of 0.073 astronomical units (1 AU is the average distance from the Earth to the Sun). That’s pretty close to the star, and Gliese 581 c would probably have a runaway greenhouse effect, similar to Venus. But right beside that is Gliese 581 d, with a mass of 7.7 Earths and an orbit of 0.22 AU. This planet could very well have liquid water on its surface.

The smallest super Earth discovered so far is MOA-2007-BLG-192Lb, which has only 3.3 times the mass of the Earth, and was orbiting a brown dwarf star. But this record will probably be beaten by the time you read this, as planet hunters get better. It’s only a matter of time before a true Earthlike planet is discovered.

We have written many articles about super Earths. Here’s an article speculating on the kinds of atmospheres that super Earths might have, and another article about how similar super Earths really are to our own planet.

Here’s an artist’s impression of a super Earth features on NASA’s Astronomy Picture of the Day website, and here’s an article from NASA about super Earths.

We also recorded an episode of Astronomy Cast dealing with the different kinds of extrasolar planets you can find. Listen to it here. Episode 125: A Zoo of Extrasolar Planets.

Source: Wikipedia

Posted on by Fraser Cain

ISS Tracking

International Space Station. Credit: NASA

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The International Space Station, or ISS, is the largest object every built by humans in space. And because it’s so large, it’s also very bright; easily visible with the unaided eye. The ISS also follows an orbital track that takes over different parts of the Earth. That means if you know the right time, you can go out and watch the station pass right over. But you need to know the right time, and that requires some kind of ISS tracking tool. Let’s take a look at some ISS tracking tools you can use to tell you when you should head outside and look up.

The best place to track ISS is from NASA’s human space flight ISS tracking page. This site will tell you the current location of the International Space Station, and space shuttles currently in flight, and the Hubble Space Telescope. The problem is that this tells you where the space station is right now, and not when it’s going to be passing through your skies… at night.

A better tool for that is the ISS sightings page. You download an applet that lets you put in your place on Earth and it gives you some upcoming dates and times that the station will be passing overhead. There’s also a quick drop down box, where you can select your location from many places in the world.

Another great tool is Heavens Above. It allows you to track the current position of thousands of satellites, including ISS and the space shuttles, when they’re in orbit.

So use one of these tools for ISS tracking, and then head outside and see if you can see the station with your own eyes.

We have written many articles about the International Space Station. Here’s an article about how you can actually see ISS in the daytime; it’s just that bright. And here’s an image of ISS and the shuttle transiting the Sun.

We have recorded an episode of Astronomy Cast that talks about the Space Station’s orbit.

Posted on by Fraser Cain

Volcanic Bombs

Lava bomb. Image credit: M. Hollunder

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A volcano erupts when hot magma from beneath the surface of the Earth breaks through the crust. Some of it comes out as lava, hot ash, gasses, pyroclastic flows, and even chunks of rock that rain down around the volcano. Any chunk of rock spewed out of a volcano that’s larger than 65 mm in diameter (2.5 inches) is considered to be a volcanic bomb, or lava bomb.

These volcanic bombs can be large, and they can be thrown tremendous distances away from the volcanic vent. In the 1935 eruption of Mount Asama in Japan, bombs measuring 5 meters in diameter were thrown 600 meters from the vent. And a volcano in Columbia killed 6 people near the summit with an eruption of volcanic bombs.

There are several different kinds of bombs that can occur, depending on the type of lava, and the force of the eruption:

  • Bread crust bombs have a cracked surface. The outer shell of the bomb cools, but the hot gasses inside are still expanding and crack the outer layer of the rock.
  • Core bombs is a chunk of lava that has cooled around some kind of solid core, like a piece of basalt. If you slice open the bomb, you’ll see the harder core, surrounded by porous pumice.
  • Cow pie bombs look like a big cow patty. They aren’t fully hardened when they hit the ground, and flatten out on impact.
  • Explosion bombs have a break in their side where hot gas inside the bomb blasted out.
  • Fusiform bombs are elongated and streamlined, forming their shape as they harden in flight
  • Ribbon bombs are long skinny strips of lava, thrown from the volcano, which then break when they impact the ground.
  • Slag bombs look like smelter slag, and have a very glassy, porous exterior.
  • Teardrop bombs look like rocky raindrops. They blast out of the volcano as liquid, and then solidify into a raindrop shape.

We have written many articles about volcanoes for Universe Today. Here’s an article about volcanoes for kids, and here’s an article about volcanic blocks; another type of rock that can be ejected from a volcano.

Here’s a great article that explains each of the different kinds of volcanic bombs in more detail. And here are some large volcanic bombs that landed around Mount Lassen.

We have recorded a whole episode of Astronomy Cast just about volcanoes. Listen to it here: Episode 141: Volcanoes, Hot and Cold.

Reference:
http://vulcan.wr.usgs.gov/Glossary/Tephra/description_tephra.html

Posted on by Fraser Cain

How Big is Pluto?

Pluto used to be the smallest planet in the Solar System, but now it isn’t a planet any more, thanks to a recent decision from the International Astronomical Union. But now it’s one of the largest dwarf planets, so that’s a good thing. How big is Pluto?

The diameter of Pluto is only 2,390 km across. Just for comparison, that’s about 70% the diameter of the Moon. And it’s a fraction of the size of the Earth; about 18% of the Earth’s diameter.

In terms of volume, Pluto only has 6.39 x 109 km3. That sounds like a huge number, but it’s only 0.59% of the volume of the Earth. In other words, you could put almost 170 objects the size of Pluto inside the Earth.

The mass of Pluto is 1.3 x 1022 kg, which is only 0.2% the mass of the Earth, or 18% the mass of the Moon. Needless to say, Pluto doesn’t have very much mass at all.

The surface area of Pluto is 1.67 x 107 square kilometers. That’s only 3.3% the surface area of Earth, and about the same surface area as Russia.

If you could stand on the surface of Pluto, you would experience only 6.7% the gravity you enjoy on Earth.

We have written many article about Pluto for Universe Today. Here’s an article that explains why Pluto isn’t a planet any more, and here are some interesting facts about Pluto.

Want more information on Pluto? Here’s Hubblesite’s News Releases about Pluto, and here’s a link to NASA’s Solar System Exploration Guide to Pluto.

We’ve recorded an entire episode of Astronomy Cast about Pluto and the rest of the icy outer Solar System. You can find it here.

Posted on by Fraser Cain

Destruction of Earth

Planet Killer
Artist's conception of an asteroid hitting Earth.

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Want to destroy the Earth? It’s harder than it sounds. That’s because the Earth is held together by the mutual gravity of 5.97 x 1024 tonnes of rock and metal. In order to blast the Earth apart, you would need to introduce more energy than the gravitational energy holding the whole planet together.

Think about it, if you wanted to bring about the destruction of Earth, you can’t just fly in your orbiting death star and fire a turbo laser at the planet. You might melt a little spot, but it’s not going to cause the planet to detonate like it did in Star Wars. Add up the mutual gravitational attraction of every atom in the Earth, and that’s how much energy you would need coming out of your laser. A laser powerful enough could vaporize the rock and metal and let it escape out into space. Keep that laser firing for billions of years and it should do the trick.

Another possibility would be to strike the Earth with an asteroid large enough to smash the planet. We’ve been hit by millions of asteroids in the past, and one was even thought to have formed the Moon. It would take an object the size of Mars slamming into Earth at more than 11 km/s to actually shatter the planet.

Instead of burning it, or smashing it, you could change the Earth’s orbit into a downward spiral into the Sun. After a few million years the planet would be burned up and destroyed by the Sun. Problem solved. In order to actually shift the Earth’s orbit, you would need to move a heavy asteroid so that it gently nudges the Earth into a spiraling orbit.

Of course, you could just bring an equivalent amount of antimatter, and let the Earth and anti-Earth collide together. The entire Earth would be annihilated in a heartbeat, leaving a flash of energy. Earth destroyed, problem solved.

But in the end, the Earth will likely be destroyed when it’s swallowed up by the Sun in about 7 billion years. When the Sun runs out of fuel, it will expand in size, becoming a red giant star. Astronomers agree it will swallow up Mercury and Venus, but they aren’t sure if it will get so large that it reaches the Earth. But whatever happens, the surface of the Earth will be scorched.

If that doesn’t completely destroy the Earth, you’ll need to wait trillions of years for the planet to get sucked into some black hole. And if that never happens, it might take 10100 years for the atoms that make up the Earth to decay into pure energy.

Then, the destruction of Earth will be complete.

This is a just a taste of the monumental amount of work it would take to bring about the destruction of Earth. Perhaps the best article every written on the subject is over here at Things of Interest.

You should also read Phil Plait’s book, Death from the Skies, which looks at all the different ways the Universe is trying to kill us.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded a two-part episode of Astronomy Cast about the End of Everything (including the Earth). Here’s part 1, and here’s part 2.

Reference:
NASA

Posted on by Fraser Cain

The Universe DVD Giveaway

In case you haven’t heard, Season 4 of the History Channel’s “The Universe” has begun. To help celebrate, they’ve generously offered to give away two sweet prizes related to the show. One person will get “The Universe Collector’s Set“, which contains Season 1, Season 2, and the 2 specials. And another person will get to choose between Season 1 on Bluray, or Season 2 on DVD.

To enter the giveaway, just email [email protected] with the Subject Line: “Universe DVD Giveaway“. I’ll collect all the entries and pick two randomly as winners. Then I’ll delete all the emails.

The deadline to enter is Monday, August 31st, 2009 at 12:00 noon (Pacific Time).

And if you want to check out The Universe now, you can buy full episodes on iTunes, order DVDs from the History Channel, and even watch it on the television. The next episode, “It Fell From Space” airs on September 1, 2009

Posted on by Fraser Cain

Which Planet Has the Most Moons?

Jupiter and its moons. Image credit: NASA/JPL

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The planet with the most moons in the Solar System is Jupiter, with a total of 63 confirmed moons (as of 2009). Of course, it’s always possible that more moons will be discovered orbiting Jupiter in the future, and that number will go up.

Eight of Jupiter’s moons are regular satellites, with 4 large, spherical moons, and 4 smaller moons that orbit closer to Jupiter. Jupiter has an additional 55 tiny irregular satellites.

The planet with the second highest number of moons is Saturn, with 61 moons. With such a close total, more moons could easily be discovered circling the rings planet, and push its total higher.

The next planet with a high number of moons is Uranus, with 27 known moons.

This is followed by Neptune with 13 moons, Mars with 2 moons, and then Earth with its single moon.

Mercury and Venus have no moons. Although Pluto isn’t a planet anymore, it does have a total of 3 moons.

We have written many articles about moons in the Solar System. Here’s an article about the largest moon in the Solar System, and here’s an article about how many moons there are in total in the Solar System.

Here’s an article from NASA about Jupiter’s moons, and here’s Hubblesite’s News Releases about Jupiter.

We have recorded a whole episode of Astronomy Cast just about Jupiter’s moons. Listen to it here.

Posted on by Fraser Cain

How Many Rings Does Uranus Have?

Uranus with its moons and rings. Image credit: Hubble

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Here’s a question, how many rings does Uranus have? Well, as of 2008, the total number of rings circling Uranus is 13.

The rings of Uranus were first discovered in 1977 by astronomers James Elliot, Edward Dunham and Douglas Mink. When he first discovered Uranus 200 years before, William Herschel reported seeing rings around Uranus, but his telescope probably wasn’t powerful enough to reveal them. Additional rings were discovered in 1986 when NASA’s Voyager 2 spacecraft made its flyby, and then two more outer rings were turned up by the Hubble Space Telescope in 2003-2005.

The rings of Uranus are dark and opaque, with a very low albedo. Astronomers believe that they’re made of water ice mixed with organic molecules. Unlike Saturn’s rings, the rings of Uranus are very narrow; just a few kilometers wide.

Uranus’ rings consist of 3 major groups. There are the narrow main rings, the dusty rings, and the newly discovered outer ring system.

Astronomers think that the rings of Uranus are being shepherded by small moons in the ring system. Without these shepherd moons, the rings of Uranus would spread out radially and dissipate into space. It’s also believed that there’s some process that’s replenishing the ice particles in the rings; perhaps collisions between icy objects in the rings.

I mentioned at the beginning of the article that current ring count stands at 13; however, that’s for 2008. With improved technology and telescopes, astronomers could turn up more rings in the future, so stay tuned.

We have written many articles about Uranus for Universe Today. Here’s an article about the discovery of new rings and moons around Uranus, and here’s an image of a blue ring around Uranus.

Here’s NASA’s Solar System Exploration Guide on the rings of Uranus, and here’s NASA’s fact sheet on the rings.

We have also recorded an entire episode of Astronomy Cast just about Uranus. Check it out here.

Posted on by Fraser Cain

Planet Earth Wallpaper

Space station above the Earth. Image credit: NASA

It’s time to redecorate your desktop with an image of the planet you live on. Here’s are a group of Planet Earth wallpapers you can use to set up as your computer background. Just click the image and you’ll see a much larger version that you can make your wallpaper. Just right-click on the full image and there should be an option to set it as your desktop.

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This wallpaper shows the International Space Station above the earth. This image was captured by the Space Shuttle during mission STS-118. You can see the Planet Earth down below.

Planet Earth seen from Messenger. Image credit: NASA
Planet Earth seen from Messenger. Image credit: NASA

This Planet Earth wallpaper was captured by NASA’s Messenger spacecraft during a flyby of Earth. It’s now visiting Mercury, helping to take incredible pictures of the planet’s surface.

Earthrise
Earthrise

Here’s a classic wallpaper of Planet Earth captured from lunar orbit. The photograph is entitled “Earthrise”, and it was captured by astronaut William Anders during an orbit of the Moon during the Apollo 8 mission.

Planet Earth wallpaper

This Earth wallpaper was captured by the Space Shuttle Discovery during mission STS-96. It shows how 3-dimensional the Earth’s atmosphere looks from orbit.

Earth lights at night.

This wallpaper shows the entire planet Earth at night. You can see how the populated areas are bright while the poorer regions of the planet are darker.