Category: Astronomy

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For all the things different about Neptune from Earth, here’s something that’s remarkably similar. The tilt of Neptune’s axis is 28.32 degrees. Compare that to the Earth’s tilt of 23.5 degrees.

With such a similar axial tilt, Neptune has very similar seasonal variations to Earth. For half of its orbit around the Sun, Neptune’s northern pole is tilted towards the Earth, and then for the other half of its orbit, the southern pole faces the Sun.

One of the biggest effects of the seasonal variation on Neptune is the current “hotspot” at Neptune’s southern pole. While most of Neptune has an average temperature of around -200 Celsius, Neptune’s south pole is about 10 degrees warmer. This makes the south pole warm enough so that methane gas – frozen in the rest of Neptune’s atmosphere – can escape into space.

Once Neptune’s seasons reverse, the hotspot will shift back to Neptune’s north pole.

We have written many stories about Neptune for Universe Today. Here’s an article about how there could be oceans deep down within Neptune’s interior, and some movies of Neptune captured by Hubble.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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We know there’s life on Earth, but could there be live on Neptune? And if there is life on Neptune, what kind of life is it?

Wherever we find liquid water on Earth, we find life. Whether that water is thousands of meters beneath the ground, inside nuclear reactors, or inside glaciers. As long as there’s water, there’s life. Of course, it’s just microbial life – but still, life.

To find life on Neptune, the planet would need to have a source of energy that bacterial life can exploit, as well as a standing source of liquid water. At its surface, the temperature of Neptune dips down to 55 Kelvin. That’s very cold, and there’s no way liquid water could exist.

But as you travel down into Neptune’s interior, temperatures and pressures increase. And there could very well be a point inside the planet where water remains as a liquid, and life could exist inside it. Of course, this region would be hundreds of kilometers below the surface, and would be impossible for us to study. So for now, it will have to remain a mystery.

Right now, scientists don’t know if there’s any life on Neptune, and the conditions on the planet seem very hostile for life. It’s unlikely we’ll ever find any there.

We wrote a detailed article on Universe Today about the possibility that there are oceans inside Neptune and other gas giant planets.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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The mass of Neptune is 1.02×10²⁶ kg.

That’s a pretty big number. If you wrote it out, it would be 102,000,000,000,000,000,000,000,000 kg. That’s still hard to wrap your brain around, so let’s give you some context. The mass of the Earth is 6 x 10²⁴ kg. In other words, the mass of Neptune is 17 times the mass of the Earth.

Neptune is actually more massive than Uranus. Uranus has only 14.5 times the mass of Earth, while Neptune has 17 times the mass of Earth.

Of course, the mass of Neptune is pretty tiny compared to some of the more massive objects in the Solar System. Neptune has only 5% the mass of Jupiter, and you could have 19,400 Neptunes to match the mass of the Sun.

We have written many stories about Neptune on Universe Today. Here’s an article about how it might have used its mass to capture Triton.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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Neptune is a gas planet, so it doesn’t have a solid surface. If you tried to walk on the surface of Neptune, you’d sink right in. But let’s say you could walk on Neptune. How strong is the gravity on Neptune? How heavy would you feel?

The surface gravity of Neptune is 1.14 times the gravity on Earth. In other words, if you could actually walk on Neptune, you would feel only a little heavier than if you were walking on Earth. If you weighed 100 kg on Earth, you would weight 114 kg on Neptune. Compare that to the much lower gravity you would feel on the Moon (16.5%) or Mars (37.6%).

Neptune has much more mass than Earth. In fact, it has a mass of 17 times the mass of the Earth. You would think that would make the gravity much more extreme. But it also has a much larger size. The diameter of Neptune is 3.8 times the diameter of Earth. This brings the gravity on Neptune down to a very comfortable 114% the gravity of Earth.

Except for the non-solid part, walking on Neptune would feel very comfortable.

Want to learn more about the gravity on the Moon, or the gravity on Mars?

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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The density of Neptune is 1.638 g/cm³.

Just to give you some comparison, the density of water is 1 g/sm³. In other words, if you had a bathtub big enough, Neptune would sink into it. This is different for Saturn which has a density of less than 1. While Neptune sinks, Saturn would float. Of course, both planets are much less dense than Earth, with a density of 5.51 g/cm³.

Want to calculate the density of Neptune on your own? It’s pretty simple math. Just take the mass of Neptune, and divide it by its volume.

The mass of Neptune is 1.0243×10²⁶ kg, and the volume of Neptune is 6.254×10¹³ km³. Divide the two, and convert to grams per cubic centimeter, and you’ll get the density of Neptune: 1.638 g/cm³.

We have written many stories about Neptune on Universe Today. Here’s an article about how there might be liquid oceans deep within Neptune. And here’s an article with cool videos of Neptune captured by Hubble.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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The diameter of Neptune is approximately 49,500 km. This makes Neptune the 4th largest planet in the Solar System, after Jupiter, Saturn and Uranus.

I say approximately because the diameter of Neptune changes depending on where you measure it. Neptune is rotating on its axis, completing a full day once every 16 hours or so. This rapid rotation flattens Neptune out slightly so that the diameter measured from pole to pole is less than the equatorial diameter.

Neptune’s polar diameter is 48,682 km. While its equatorial diameter is 49,528 km. In other words, points on the equator are 423 km more distant from the center of Neptune than the poles.

Want some comparison? The diameter of Neptune is about 3.9 times the diameter of Earth.

We have written many stories about Neptune for Universe Today. Here’s an article about how Neptune’s south pole is the warmest part of the planet.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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A day on Neptune is 16 hours, 6 minutes and 36 seconds.

Wait, not so fast! Here’s the problem. Neptune isn’t a single solid object like the terrestrial planets, so different parts of the planet rotate at different speeds. This is a process that astronomers call differential rotation. Neptune’s equatorial zone takes about 18 hours to complete a rotation – that’s slower than the planet’s averate 16.1 hour rotation period. And the polar regions can take just 12 hours to rotate; much more quickly than the average.

This big difference in rotational rate between the equatorial regions and the planet’s poles means that Neptune has a strong latitudinal wind shear. This helps to generate the strongest winds in the Solar System. Astronomers have clocked winds on Neptune going as fast as 2,400 km/hour (1,500 miles/hour).

We have done several stories about Neptune on Universe Today. Here’s an article about movies of Neptune captured by Hubble. These show its rotation.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

The color of Neptune is a bright azure blue. During its flyby in 1989, NASA’s Voyager 2 revealed the bright blue color, different from the pale blue color of Uranus. So why does Neptune have this color?

The answer to Neptune’s color comes from its cloud tops. The upper atmosphere of Neptune is made up of 80% hydrogen, 19% helium with a trace 1% amount of methane and other ices, like ammonia and water. Methane absorbs light at 600 nm, which is the red end of the spectrum of visible light.

Like all the planets in the Solar System, the light we see coming from Neptune is actually reflected light from the Sun. These methane clouds absorb the red end of the spectrum, and allow the blue end of the spectrum to bounce back out. So when you see the color of Neptune, you’re seeing reflected sunlight with the red light stripped out.

From a distance, Neptune looks just like a blue ball, but as you get closer you can see variations in its clouds. Lighter clouds of methane hang above the lower cloud deck. Powerful storms whip across the surface of Neptune; the fastest storms in the Solar System are on Neptune, with winds exceeding 2,400 km/hour. Neptune has a large dark storm, similar to the Great Red Spot on Jupiter.

We have written many articles about Neptune on Universe Today. Here’s an article about “movies” of Neptune captured by Hubble. And some additional images captured by Hubble that really show the color of Neptune.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.