Author: Fraser Cain

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Are you planning a trip to the Moon and you’re wondering what kinds of temperature you might experience. Well, you’re going to want to pack something to keep you warm, since the temperature of the Moon can dip down to -153°C during the night. Oh, but you’re going to want to keep some cool weather clothes too, since the temperature of the Moon in the day can rise to 107°C.

Why does the moon’s temperature vary so widely? It happens because the Moon doesn’t have an atmosphere like the Earth. Here on Earth, the atmosphere acts like a blanket, trapping heat. Sunlight passes through the atmosphere, and warms up the ground. The energy is emitted by the ground as infrared radiation, but it can’t escape through the atmosphere again easily so the planet warms up. Nights are colder than days, but it’s nothing like the Moon.

There’s another problem. The moon takes 27 days to rotate once on its axis. So any place on the surface of the Moon experiences about 13 days of sunlight, followed by 13 days of darkness. So if you were standing on the surface of the Moon in sunlight, the temperature would be hot enough to boil water. And then the Sun would go down, and the temperature would drop 250 degrees in just a matter of moments.

To deal with this dramatic range in temperature, spacesuits are heavily insulated with layers of fabric and then covered with reflective outer layers. This minimizes the temperature differences between when the astronaut is in the sunlight and when in shade. Space suits also have internal heaters and cooling systems, and liquid heat exchange pumps that remove excess heat.

There are craters around the north and south poles of the Moon which are bathed in complete shadow, and never see sunlight. This places would always be as cool as -153°C. Similarly, there are nearby mountain peaks which are bathed in continuous sunlight, and would always be hot.

We have written many articles for Universe Today about some of the special regions of the Moon. Here’s an article about building a moon base, and here’s an article about a perfect crater for a human settlement.

Here’s an answer to the question from Windows on the Universe, and here’s some information from Teacher’s Domain.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

Reference:
NASA Moon Facts

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The Moon has no atmosphere. None. That’s why astronauts have to wear their spacesuits when they get outside of their spacecraft on the surface of the Moon.

Okay… that’s not exactly true. The Moon does have a tiny atmosphere. If you could capture the entire atmosphere of the Moon, and pile it up, you would get a total mass of 10,000 kg. In other words, the entire mass of the atmosphere of the Moon weighs less than a large truck.

This lunar atmosphere comes from a few sources. One source for the atmosphere is outgassing, from radioactive decay processes deep inside the crust and mantle of the Moon. Another comes from debris kicked up by micrometeorite impacts on the surface of the Moon.

This creation of the atmosphere through impacts is known as “sputtering”. Earth-based telescopes have detected sodium and potassium in a diffuse cloud around the Moon, and NASA’s Lunar Prospector spacecraft detected radon-222 and polonium-201. Finally, detectors carried by the Apollo astronauts turned up argon, helium, oxygen, methane, nitrogen, carbon monoxide and carbon dioxide. But you’ve got to appreciate that these are in extremely low quantities.

One final atmosphere of the Moon might be electrostatically levitated moon dust. These tiny particles are constantly leaping up and down off the surface of the Moon. On the daylight side of the Moon, solar ultraviolet and X-ray radiation knocks electrons out of atoms in the lunar soil. This makes them build up a positive charge until they’re repelled from the surface and might launch meters or even kilometers above the surface of the Moon before falling back down.

But even with all these trace elements, the Moon really has no atmosphere at all. If you stepped outside of your spacecraft and onto the lunar surface without a spacesuit to provide you with an atmosphere, you would die in less than a minute.

Here are some articles about other moons that do have atmospheres. Here’s Saturn’s moon Enceladus, and Saturn’s moon Titan.

Here’s an article from Windows on the Universe about how static forces make dust jump on the Moon, and here’s an article from Astronomy 121.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

References:
http://lunar.arc.nasa.gov/project/faq.htm
http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html

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How old is the Moon? Almost the entire Solar System formed 4.6 billion years ago, when the solar nebula collapsed. But astronomers think that the Moon formed later than that, when a Mars-sized protoplanet smashed into the Earth. The debris from the collision splashed into orbit around the Earth and then reformed into the Moon, which still orbits us today.

So when did this happen?

Astronomers think this collision happened about 4.53 billion years ago, about 30-50 million years after the rest of the Solar System formed. This was relatively soon after the formation of the Solar System, and well before the time when life formed on Earth. Our planet was probably still mostly a molten ball of rock, and the impact of the Moon did little to change that. This is the dominant theory of how the Moon formed, but there are others. It’s possible that the Moon was captured by the Earth’s gravity, or it just formed in place around the Earth after the formation of the Solar System.

Evidence for this collision was found by the astronauts of the Apollo Moon landing missions. They turned up lunar rocks that have oxygen isotope compositions which are nearly the same as the Earth. This means that portions of the Moon were once part of the Earth. Scientists announced their findings in 1969 in the journal Science, saying that the Moon was at least 4 billion years old.

More recent research measured tungsten content in rocks returned from the moon. Tungsten-182 is what you get when hafnium-182 decays. So the scientists measured the ratios of tungsten to hafnium to determine exactly when the moon formed. This is where the number 4.527 billion years (give or take 10 million years).

One problem with this technique is that it’s based on the relative age of meteorites used to determine how old the Solar System is. If that research is incorrect, these estimates for the age of the Moon might be incorrect too.

We have written many articles about the Moon for Universe Today. Here’s an article about the giant impactor theory, and here’s an article about how scientists link the formation of the Earth and the Moon.

Here’s an article that talks about how the age of the Moon was determined. And some history from Stony Book labs, the people who analyzed the first moon rocks.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

References:
http://www.armaghplanet.com/pdf/AstroTopics/Solar%20System/Deeptime.pdf
http://pubs.usgs.gov/gip/geotime/age.html

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Everything we know about Uranus comes from looking through a telescope. Only one spacecraft, Voyager 2, has ever made a close flyby of the planet. Astronomers suspect there is lots of water on Uranus. Since they’ve never actually sampled the surface of the planet, how could they know?

It all comes down to density.The density of Uranus is the second least in the Solar System, after Saturn. In fact, it has a density that’s only a little higher than water. Since water is very common in the outer Solar System, astronomers suspect that the whole planet is made of mostly water. But it’s not like any water you’ve ever seen.

The temperature at the cloud tops of Uranus is 57 K (-357 F), and that temperature increases as you go down at a very predictable rate. It’s believed that the temperature at the center of Uranus is about 5,000 K. Liquid water can’t survive those kinds of temperatures without boiling away, unless you hold it under huge pressure. The water should be a vapor, but the heat and pressure turns it into a superheated liquid.

Did you know that there might be oceans on Neptune? Here’s an article about it.

And here’s some more information about water on Uranus from the Internet. NASA has an article that talks about superheated water on Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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Uranus is one of the strangest planets in the Solar System. Something huge smashed into the planet billions of years ago and knocked it over on its side. While the other planets look like spinning tops as they make their journey around the Sun, Uranus is flipped on its side, and appears to be rolling around the Sun. And this has a dramatic effect on the seasons on Uranus.

The Earth’s tilt gives us our seasons. When the northern hemisphere is tilted towards the Sun, that’s summer. And when it’s tilted away from the Sun, that’s winter for the northern hemisphere. But on Uranus, one hemisphere is pointed towards the Sun, and the other is pointed away. The position of the poles slowly reverse until, half a Uranian year later, it’s the opposite situation. In other words, summer for the northern hemisphere lasts 42 years long, followed by 42 years of winter.

If you could stand at the north pole of Uranus (you can’t, you’d sink right in), you would see the Sun appear on the horizon, circle higher and higher for 21 years and then circle back down to the horizon over the course of another 21 years. Once the Sun went below the horizon, you would experience another 42 years of darkness before the Sun appeared again.

You would expect this bizarre configuration to give Uranus wild seasons; the day side faces the Sun and the atmosphere never rotates to the night side to cool down. The night side is in darkness, and the atmosphere never gets a chance to warm up. As the Sun first shines on a region that was cold and dark for years, it heats it up, generating powerful storms in the atmosphere of Uranus. Early observers reported seeing bands of cloud on Uranus through their telescopes, but when NASA’s Voyager 2 spacecraft arrived, it was blue and featureless. It might be that the changing seasons will bring the storms back to Uranus.

Want to learn about the seasons on other planets? Here’s are the seasons on Mars, and the seasons on Saturn.

Here’s an article from the BBC about the changing seasons on Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

We’re all familiar with the beautiful rings around Saturn. In fact, you can see them with any backyard telescope. But did you know that Uranus has rings too?

The rings of Uranus were first discovered in 1977 by the astronomical team of James L. Elliot, Edward W. Dunham, and Douglas J. Mink. When he first discovered Uranus more than 200 years ago, William Herschel also reported seeing rings, but that’s probably impossible, because the rings of Uranus are very dark and thin.

Astronomers now know that Uranus has 13 distinct rings. They start at about a distance of 38,000 km from the center of Uranus, and then extend out to about 98,000 km.

Unlike the rings of Saturn, which are very bright and composed of water ice, the rings of Uranus are relatively dark. Instead of containing dust, the rings seem to be made up of larger chunks, measuring 0.2 to 20 m across. These would really qualify as boulders, not dust. They’re also very thin. Each ring is only a few km thick.

Uranus now has a total of 10 known rings.

The rings of Uranus are thought to be very young, not more than 600 million years old. They probably came from a few shepherd moons that were shattered by Uranus’ gravity and turned into rings around the planet. The chunks collided with each other and turned into smaller and smaller particles.

We have written many stories about the rings of Uranus. Here’s one about the rings seen edge on. And here’s another about the discovery of a blue ring around Uranus.

Here’s an article that discusses the discovery of the Rings of Uranus. And here’s a fact sheet from NASA about Uranus’ rings.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

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The more we learn about life on Earth, the more we realize that it can live in some of the most inhospitable places on the planet: encased in ice, in boiling water, and even in places with high radiation. But could life exist elsewhere in the Solar System? Could there be life on Uranus?

Maybe, but probably not.

There are a few problems. The first is the fact that Uranus has no solid surface. It’s mostly composed of ices: methane, water and ammonia. And then it’s enshrouded by an atmosphere of hydrogen and helium. The second is that Uranus is really cold. Its cloud tops measure 49 K (?224 °C), and then it gets warmer inside down to the core, which has a temperature of 5,000 K.

You could imagine some perfect place inside Uranus, where the temperature could support life. The problem is that the pressures inside Uranus are enormous at those temperatures, and would crush life. The other problem is that life on Earth requires sunlight to provide energy. There’s no process inside Uranus, like volcanism on Earth, that would give life inside the planet a form of energy.

Life on Uranus would have to be vastly different from anything we have here on Earth to be able to survive. Of course, it’ll be almost impossible to ever send a spacecraft down into the planet to look for ourselves.

We have written many articles about the search for life in the Solar System. Here’s an article about how life on Mars might have been killed off. And here’s an article about how the soil on Mars might have supported life.

Here’s a link to Hubblesite’s News Releases about Uranus, and here’s NASA’s Solar System Exploration guide.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.

How’s the temperature on Uranus? Cold. In fact, the temperature of Uranus makes it the coldest planet in the Solar System. The average temperature of the cloud tops on Uranus is 49 K (?224 °C).

Why is Uranus so cold? The big problem is that Uranus isn’t generating any heat. The other giant planets in the Solar System actually give off more heat than they receive from the Sun. This is because they’re slowly compacting down, and this generates high temperatures inside their cores. Uranus has a core of only 5,000 K, while Jupiter’s core is 30,000 K. If you removed the Sun, Jupiter would still be visible in infrared telescopes because of this internal warmth, but Uranus would be very dark.

Astronomers aren’t sure why Uranus has such a low core temperature, but they think it has something to do with its bizarre rotation. Unlike the rest of the planets in the Solar System, Uranus is tilted right over onto its side. Scientists think that Uranus has a massive collision early on in its history, which knocked it over. This collision might have also allowed the planet to release much of its internal heat. Others believe that something about Uranus’ internal structure allows it to release this heat more easily than other planets.

We have written many articles about Uranus here on Universe Today. Here’s an article about how Uranus can actually get pretty stormy, and here’s an article about what should be found inside a gas giant.

If you’d like more info on Uranus, check out Hubblesite’s News Releases about Uranus. And here’s a link to the NASA’s Solar System Exploration Guide to Uranus.

We have recorded an episode of Astronomy Cast just about Uranus. You can access it here: Episode 62: Uranus.