Posted on by Fraser Cain

US Space Missions

Missions

The United States has launched dozens of missions into space. Most people can only recall two with ease: Apollo 11 because it landed on the moon, though few can tell you its Apollo 11, just that Neil Armstrong landed on the Moon and the shuttle Challenger because it exploded so dramatically.

Over the course of 6 decades NASA, and its predecessor NACA, has launched 30 missions within projects Mercury and Gemini, not to mention the countless flights made by the five space shuttles. Every mission flown had at least on ‘first’: first in low Earth orbit, first in orbit, first to orbit the Moon, first American in space, and so on. In order to carefully list the accomplishments of each mission would take several hundred pages, so here on Universe Today we have compiled a list of links to articles about each mission. To shorten the list even further, we cut out some of the missions that were scrubbed or did not launch.

You will also find some links to unmanned flights like the Voyager project, Cassini, and the Mars rovers.

Be sure to follow as many of the links below as possible. You will discover many new and interesting facts about the American space program.

Uncrewed Space Flight

Crewed Spaceflight

Posted on by Fraser Cain

Axis Tilt of Neptune

Neptune from Voyager 2. Image credit: NASA/JPL

[/caption]
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.

Posted on by Fraser Cain

Life on Neptune

Neptune, captured by Voyager 2. Image credit: NASA

[/caption]
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.

Posted on by Fraser Cain

Mass of Neptune

Neptune compared to Earth. Image credit: NASA

[/caption]
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.

Posted on by Fraser Cain

Pictures of Neptune

Neptune from Voyager 2. Image credit: NASA/JPL

Here is a collection of all the best pictures of Neptune captured by Voyager 2, Hubble and Earth-based telescopes. Unfortunately, only one spacecraft, Voyager 2, has ever visited Neptune up close, so all the closeup images of Neptune were captured over the course of just a few days as Voyager 2 swept by the planet in 1989.

[/caption]
This is a classic picture of Neptune captured by NASA’s Voyager 2 spacecraft during its 1989 flyby of Neptune. The NASA spacecraft had already visited Jupiter, Saturn and Uranus during its trip, and Neptune was the final stop on its grand tour of the planets before speeding off into deep space. You can see a giant storm raging on the surface of Neptune, which scientists have named Neptune’s Great Dark Spot.

Neptune and its Great Dark Spot. Image credit: NASA/JPL
Neptune and its Great Dark Spot. Image credit: NASA/JPL

Here’s an amazing pic of Neptune captured by Voyager 2. In this image, the planet’s Great Dark Spot is much more visible. You can also see a white storm around the rim of the great dark spot, which scientists call a “scooter”.

Neptune seen by Hubble. Image credit: Hubble
Neptune seen by Hubble. Image credit: Hubble

This Neptune photo was captured by the mighty Hubble Space Telescope. It shows just how powerful and sensitive Hubble is. Keep in mind that Neptune is 4.5 billion kilometers away from Earth. Another interesting feature is the fact that the dark spot seems to be missing in this image of Neptune.

Clouds above Neptune. Image credit: NASA/JPL
Clouds above Neptune. Image credit: NASA/JPL

This amazing Neptune pic shows distinct clouds hovering above Neptune’s lower cloud deck. You can even see shadows cast onto the surface of Neptune by these clouds. Astronomers think that the clouds are made of methane gas. This image of Neptune was captured by NASA’s Voyager 2 during its 1989 Neptune flyby.

Neptune's largest Moon, Triton. Image credit: NASA/JPL
Neptune's largest Moon, Triton. Image credit: NASA/JPL

This is an incredible image of Neptune’s largest moon Triton, which was also seen by Voyager during its 1989 flyby of Neptune and its moons. It was captured at an altitude of 146,000 km above the surface of Triton.

Neptune seen from Earth. Image credit: Keck
Neptune seen from Earth. Image credit: Keck

And finally, here’s a Neptune picture captured from Earth. It was taken by the Keck II telescope in Hawaii. This is one of the largest telescopes in the world, and it’s equipped with an adaptive optics instrument that allows the telescope to remove the blurring effects of the Earth’s atmosphere.

Posted on by Fraser Cain

Gravity on Neptune

Neptune compared to Earth. Image credit: NASA

[/caption]
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.

Posted on by Fraser Cain

How Far is Neptune from Earth?

Neptune, captured by Voyager 2. Image credit: NASA

[/caption]
Here’s a quick answer: Neptune is approximately 4.4 billion km away from the Earth.

Have you ever wondered how far Neptune is from the Earth? It’s actually a bit of a trick question. That’s because the distance between Neptune and Earth is constantly changing, depending on where they are in their orbits around the Sun.

It gets even more complicated, because both Earth and Neptune follow the Sun on elliptical orbits. They both have a closest point to the Sun, called perihelion, and a distant point, called aphelion.

So, the closest point occurs when Earth and Neptune are on the same side of the Sun. Earth is at its most distant point from the Sun, and Neptune is at its closest. At this point, Earth and Neptune are separated by only 4.301 billion kilometers.

At their most distant point, Earth and Neptune are on opposite sides of the Sun, at the most distant points on their orbits. At this point, Earth and Neptune are separated by 4.553 billion kilometers.

If you’re interested, here’s an article that lists how far away all the planets are from the Sun and Earth.

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.

Posted on by Fraser Cain

Density of Neptune

Composition of Neptune. Credit: NASA

[/caption]
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.

Posted on by Fraser Cain

Diameter of Neptune

Neptune compared to Earth. Image credit: NASA

[/caption]
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.

Posted on by Fraser Cain

How Long is a Day on Neptune?

Rotation of Neptune. Image credit: Hubble

[/caption]
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.