Posted on by Fraser Cain

How Big is Jupiter?

Hubble Jupiter

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I’m sure you’ve heard that Jupiter is the largest planet in the Solar System, but just how big is Jupiter?

In terms of size, Jupiter is 142,984 km (88,846 miles) in diameter across its equator. If you just compare that to Earth, it’s 11.2 times the diameter of Earth. But then, it’s only 10% the diameter of the Sun.

The volume of Jupiter is 1.43128×1015 km3. That’s enough to fit inside 1321 planets the size of Earth, and still have room left over.

The surface area of Jupiter is 6.21796×1010 km2. And just for comparison, that’s 122 times more surface area than Earth.

And finally, the mass of Jupiter is 1.8986×1027 kg. That’s enough mass for 318 Earths. In fact, Jupiter is 2.5 times more than the mass of all the other planets in the Solar System. But then, the Sun accounts for 99.9% of the mass of the Solar System.

Jupiter’s big, no question, but don’t worry about the possibility that Jupiter might become a star. It would need another 80 times its own mass to be able to ignite solar fusion.

We’ve written several articles about Jupiter for Universe Today. Here’s an article about an impact that recently happened on Jupiter, and here’s an article about how Jupiter might protect us in the Solar System.

If you’d like more information on Jupiter, check out Hubblesite’s News Releases about Jupiter, and here’s a link to NASA’s Solar System Exploration Guide to Jupiter.

We’ve also recorded a whole episode of Astronomy Cast just about Jupiter. Listen here, Episode 56: Jupiter.

Posted on by Fraser Cain

What is Jupiter’s Great Red Spot?

Jupiter's Red Spot

One of the most prominent features in the Solar System is Jupiter’s Red Spot. This is a massive storm three times the size of the Earth that has been raging across the cloud tops of Jupiter since astronomers first looked at it with a telescope.

Known as the Great Red Spot, this is an anticyclonic (high pressure) storm that rotates around the planet at about 22°. Astronomers think that its darker red color comes from how it dredges up sulfur and ammonia particles from deeper down in Jupiter’s atmosphere. These chemicals start out dark and then lighten as they’re exposed to sunlight. Smaller storms on Jupiter are usually white, and then darken as they get larger. The recently formed Red Spot Jr. storm turned from white to red as it grew in size and intensity.

Astronomers aren’t sure if Jupiter’s Red Spot is temporary or permanent. It has been visible since astronomers started making detailed observations in the 1600s, and it’s still on Jupiter today. Some simulations have predicted that this a storm like this might be a permanent fixture on Jupiter. You can still see the Red Spot with a small telescope larger than about 15 cm (6 inches).

The edge of the Red Spot is turning at a speed of about 360 km/h (225 mph). The whole size of the spot is ranges from 24,000 km x 12,000 km to as wide as 40,000 km. You could fit two or three Earths inside the storm. The actual edge of the storm lifts up about 8 km above the surrounding cloud tops.

Astronomers have noticed that it’s been slowly shrinking over the last decade or so, losing about 15% of its total size. This might be a temporary situation, or Jupiter’s Red Spot might go on losing its size. If it continues, it should look almost round by 2040.

We’ve written many articles about Jupiter’s Red Spot for Universe Today. Here’s an article about Jupiter’s little red spot, and here’s an article about Jupiter’s red spot colliding together.

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

We’ve also recorded an episode of Astronomy Cast all about Jupiter. Listen here, Episode 56: Jupiter.

Posted on by Fraser Cain

Earth’s Mass

Blue Marble Earth

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The Earth’s mass is 5.9736 x 1024 kg. That’s a big number, so let’s write it out in full: 5,973,600,000,000,000,000,000,000 kg. You could also say the Earth’s mass is 5.9 sextillion tonnes. Phew, that’s a lot of mass.

That sounds like a lot, and it is, but the Earth has a fraction of the mass of some other objects in the Solar System. The Sun has 333,000 times more mass than the Earth. And Jupiter has 318 times more mass. But then there are some less massive objects too. Mars has only 11% the mass of the Earth.

Because of its high mass for its size, Earth actually has the highest density of all the planets in the Solar System. The density of Earth is 5.52 grams per cubic centimeter. The high density comes from the Earth’s metallic core, which is surrounded by the rocky mantle. Less dense planets, like Jupiter, are just made up of gases like hydrogen.

We’ve written several articles about the mass of planets in the Solar System. Here’s an article about the mass of Mercury, and here’s an article about the mass of the Sun.

If you’d like more information on the Earth mass, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about the Earth. Listen here, Episode 51: Earth.

Posted on by Fraser Cain

Mars Global Surveyor

Mars Global Surveyor

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The Mars Global Surveyor was a spacecraft sent to Mars in 1996. It arrived at Mars and studied the planet for 10 years, until it broke down in 2006, and controllers on Earth lost contact with it. But while it was operating, the spacecraft took thousands of images, and made some major discoveries about Mars.

Mars Global Surveyor was launched on November 7, 1996, and made its orbital insertion on September 11, 1997. It used a technique called aerobraking to reduce its orbit and bring it into an orbit that brought it to an average distance of 378 km from the surface of Mars. It circled the planet in a polar orbit once every 117 minutes, which allowed it to photograph the entire Martian surface.

The spacecraft was equipped with 5 major scientific instruments: Mars Orbiter Camera, Mars Orbiter Laser Altimeter, Thermal Emission Spectrometer, Magnetometer and electron reflectometer and the Ultrastable Oscillator for Doppler measurements. These instruments allowed the spacecraft to study the atmosphere and surface composition of Mars. But it also sent back the highest resolution photographs ever seen of Mars. The newer Mars Reconnaissance Orbiter has returned better images with its larger telescope, but when the first MGS images first came back from Mars, they were stunning.

It made some incredible discoveries about Mars. Thanks to the observations from MGS, astronomers determined that Mars had a layered crust that was more than 10 km thick. It found ancient craters that had been buried and then later exposed by erosion, and it found evidence of ancient lava flows.

But perhaps the biggest discovery was made in 2006, which researchers announced that they had uncovered evidence of recent water activity on Mars. Images from the Mars Global Surveyor showed gullies on Mars which looked like they’d been formed by water. It’s possible that water had erupted out of an underground aquifer and spilled down the slope of a hill before evaporating in the pressure of the Martian atmosphere.

After a decade of service, Mars Global Surveyor went silent on November 2, 2006. It went into safe mode after being issued commands to change the orientation of its solar panels, and it stopped communicating. NASA said that it was, “battery failure caused by a complex sequence of events involving the onboard computer memory and ground commands.” But we’ll never really know what happened to it.

We’ve written many articles about the Mars Global Surveyor for Universe Today. Here’s an article about how we lost contact with the Mars Global Surveyor, and here’s a picture of Earth taken by MGS.

If you’d like more info, check out the Mars Global Surveyor homepage.

Source: NASA

Posted on by Fraser Cain

Blood Moon



A blood moon is the first full moon after a harvest moon, which is the full moon closest to the fall equinox. Another name for a blood moon is a hunter’s moon.

Before the advent of electricity, farmers used the light of the full moons to get work done. The harvest moon was a time they could dedicate to bringing in their fall harvest. And so a month later is the blood moon, or the hunter’s moon. This was a good time for hunters to shoot migrating birds in Europe, or track prey at night to stockpile food for Winter.

A full moon occurs every 29.5 days, so a blood moon occurs about a month after the harvest moon. A blood moon is just a regular full moon. It doesn’t appear any brighter or redder than any other full moon. The distance between the Earth and the Moon can change over the course of the month. When the moon is at its closest, a full moon can appear 10% larger and 30% brighter than when it’s further away from the Earth.

A blood moon will actually turn red when it matches up with a lunar eclipse. These occur about twice a year, so blood moons match up with lunar eclipses about every 6 years or so. At the time of this writing, the next blood moon lunar eclipse will be in 2015.

We’ve written many articles about the Moon for Universe Today. Here’s an article about the discovery of water on the Moon, and here’s an article about a lava tube on the Moon.

If you’d like more info on the Moon, check out NASA’s Solar System Exploration Guide on the Moon, and here’s a link to NASA’s Lunar and Planetary Science page.

We’ve also done several episodes of Astronomy Cast about the Moon. Here’s a good one, Episode 17: Where Does the Moon Come From?

Posted on by Fraser Cain

The Eye of God

Helix Nebula

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There was an email going around a few years ago talking about “the Eye of God”. This photo was actually an image of the Helix Nebula taken by the Hubble Space Telescope.

The Eye of God nebula is a bright planetary nebula located about 700 light-years away in the constellation Aquarius; it’s also known as NGC 7293. In fact, the Helix Nebula is probably the closest planetary nebula we can see in the sky, and it shows the future that stars like our Sun go through when they run out of fuel and puff out their outer layers.

It’s thought that the Helix Nebula is actually cylindrical shaped. From our perspective, we’re looking down the cylinder to see the central star. Astronomers estimate that the Helix Nebula is about 10,600 years old, based on the rate of expansion of the nebula.

With the power of the Hubble Space Telescope, astronomers were able to see knots of material in the nebula. They’ve now discovered more than 20,000 of these cometary knots in the nebula. These knots have cometary tails, and it’s been discovered that they can collide with one another.

Here’s the email you might get:

Subject: Fw: Eye of God
This is a picture taken by NASA with the Hubble telescope. They are referring to it as the “Eye of God”. I thought it was beautiful and worth sharing.

Some emails even say that this is a rare event that only happens once every 3,000 years. The reality is that this is just a beautiful photograph taken by the Hubble Space Telescope. There are other images that have been taken by other telescopes and they look beautiful as well.

We’ve written several articles about the Helix Nebula for Universe Today. Here’s an article about a new view into the Helix Nebula, and here’s an article about comets colliding inside the Helix Nebula.

If you’d like more info on the Helix Nebula, here’s a nice picture from the La Silla Observatory at Astronomy Picture of the Day.

We’ve also recorded an entire episode of Astronomy Cast just about nebulae. Listen here, Episode 111: Nebulae.

Posted on by Fraser Cain

Artificial Satellites

It's getting crowded out there: active and inactive satellites are tracked (Google/Analytical Graphics)

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Artificial satellites are human-built objects orbiting the Earth and other planets in the Solar System. This is different from the natural satellites, or moons, that orbit planets, dwarf planets and even asteroids. Artificial satellites are used to study the Earth, other planets, to help us communicate, and even to observe the distant Universe. Satellites can even have people in them, like the International Space Station and the Space Shuttle.

The first artificial satellite was the Soviet Sputnik 1 mission, launched in 1957. Since then, dozens of countries have launched satellites, with more than 3,000 currently operating spacecraft going around the Earth. There are estimated to be more than 8,000 pieces of space junk; dead satellites or pieces of debris going around the Earth as well.

Satellites are launched into different orbits depending on their mission. One of the most common ones is geosynchronous orbit. This is where a satellite takes 24 hours to orbit the Earth; the same amount of time it takes the Earth to rotate once on its axis. This keeps the satellite in the same spot over the Earth, allowing for communications and television broadcasts.

Another orbit is low-Earth orbit, where a satellite might only be a few hundred kilometers above the planet. This puts the satellite outside the Earth’s atmosphere, but still close enough that it can image the planet’s surface from space or facilitate communications. This is the altitude that the space shuttle flies at, as well as the Hubble Space Telescope.

Artificial satellites can have a range of missions, including scientific research, weather observation, military support, navigation, Earth imaging, and communications. Some satellites fulfill a single purpose, while others are designed to perform several functions at the same time. Equipment on a satellite is hardened to survive in the radiation and vacuum of space.

Satellites are built by various aerospace companies, like Boeing or Lockheed, and then delivered to a launch facility, such as Cape Canaveral. Launch facilities are located as close as possible to the Earth’s equator, to give an extra velocity kick into space. This allows rockets to use less fuel or launch heavier payloads.

The altitude of a satellite’s orbit defines how long it will stay in orbit. Low orbiting satellites are mostly above the Earth’s atmosphere, but they’re still buffeted by the atmosphere and their orbit eventually decays and they crash back into the atmosphere. Other satellites orbiting in high orbits will likely be there for millions of years.

We’ve written many articles about artificial satellites for Universe Today. Here’s an article about geosynchronous orbit, and here’s an article about orbital speed.

You can get more information about satellites from NASA. Here’s a cool realtime satellite tracking system, and here’s Hubblesite.

We’ve also recorded several episodes of Astronomy Cast about satellites. Here’s a good one, Episode 82: Space Junk.

Source: NASA

Posted on by Fraser Cain

Tenth Planet: The Next World in the Solar System

Tenth planet? Artists concept of the view from Eris with Dysnomia in the background, looking back towards the distant sun. Credit: Robert Hurt (IPAC)
Tenth planet? Artists concept of the view from Eris with Dysnomia in the background, looking back towards the distant sun. Credit: Robert Hurt (IPAC)

Before 1930, there were 8 planets in the Solar System. And then with the discovery of Pluto in 1930, the total number of planets rose to 9. Although astronomers kept searching for more planets, it wasn’t until 2005 that an object larger than Pluto was found orbiting in the distant Solar System. This new object was known as Eris, and many considered it to be a tenth planet; but it actually created a controversy that ended up with Pluto being kicked out of the planet club and becoming a dwarf planet. There really is no 10th planet, in fact, we don’t even have a ninth planet any more.

Discovery of Eris

Eris, originally named 2003 ub 313 was discovered by Palomar observatory researcher Mike Brown; Mike has been behind many of the trans-Neptunian discoveries in the last decade. Mike and his team discovered Eris by systematically scanning the sky for objects moving at the right speed in the right object to be in the outer Solar System.

Further observations of Eris showed that it was actually larger than Pluto by a significant amount; it measured 2,500 km across, compared to Pluto’s 2,300 km diameter. And it orbited at a distance of 67 astronomical units, compared to Pluto’s 39 AU (1 AU is the average distance from the Earth to the Sun).

Tenth Planet, Dwarf Planet

Because there was now a larger object than Pluto found orbiting the Sun, astronomers needed to decide whether this would be come the tenth planet. At a meeting of the International Astronomical Union in 2006, astronomers decided to redefine their classification of a planet. And these new rules excluded Eris. Instead of becoming the tenth planet, Eris became a dwarf planet; the same fate as Pluto.

We’ve written many articles about Eris for Universe Today. Here’s an article about how Eris is changing, and here’s an article about how Xena was renamed to Eris.

If you’d like more info on Eris, check out NASA’s page on Eris.

We’ve also recorded an episode of Astronomy Cast that explains why Pluto isn’t a planet any more. Listen here, Episode 1: Pluto’s Planetary Identity Crisis.

Posted on by Fraser Cain

Life of a Star

Artist’s impression of a baby star still surrounded by a protoplanetary disc in which planets are forming. Credit: ESO

Stars are kind of like people. They’re born, they live their lives, and then they die. Let’s take a look at the life of a star.

All stars start out a giant clouds of neutral hydrogen, which has been left over since the Big Bang. Some event, such as a nearby supernova explosion causes the cloud to collapse inward, and then gravity takes over. As the cloud collapses, it breaks up into different knots of material, each of which will go on to form a star.

As the cloud continues to collapse inward, the conservation of angular momentum from all the particles sets the cloud spinning. As gravity pulls it further inward, it begins spinning faster and faster and flattens out into a disk. The star forms from the concentration of material in the center of the protostellar disk, and the planets form out in the disk.

In the beginning, a star shines because of the heat of compression through gravity. But eventually the core of the star heats up to the point that nuclear fusion reactions can occur. At this point, the star blasts away the remaining dust and gas with its solar winds and enters the main sequence phase of life.

A star like our Sun will continue as a main sequence star for billions of years; slowly converting hydrogen into helium in its core. But it will eventually run out of easily usable hydrogen in its core. When this happens, the star collapses down a little and then starts to convert a shell of hydrogen into helium around the core. This additional heat puffs out the star into a red giant, causing it to become much larger.

A typical star will go through several phases of expansion and contraction as it burns through shells of hydrogen around its core. Larger stars will also switch to helium fusion in the core, and even go up the periodic table of elements, fusing heavier and heavier elements. Eventually they’ll reach the limits of gravity, running out of fuel to burn. The star will then slough off its outer layers, creating the beautiful planetary nebulae we see from Earth.

And then the star will collapse inward, becoming a white dwarf star. This is a highly compressed object that can have the mass of the Sun, but only be as small as the Moon. It’s still hot because of the residual energy it had when it was a true star, but it slowly cools down, eventually becoming a black dwarf; the same temperature as the background of the Universe.

Stars much larger than our own Sun can have a more dramatic finish. The largest stars will detonate as supernovae when they reach the end of their lives. Some will then collapse down to become neutron stars or black holes, while others explode with such energy that the entire star just blows itself apart.

We’ve written many articles about stars for Universe Today. Here’s an article about the death of stars, and here’s an article about the life cycle of stars.

If you’d like more information on stars, check out Hubblesite’s News Releases about Stars, and here’s the stars and galaxies homepage.

We’ve also recorded several episodes of Astronomy Cast about stars. Here’s a good one, Episode 12: Where Do Baby Stars Come From?

Source: NASA

Posted on by Fraser Cain

Retrograde

Neptune's largest Moon, Triton. Astronomers think that Triton is a captured Kuiper Belt Object. Credit: NASA/JPL

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When objects in the Solar System orbit other objects, they can either go in a regular prograde direction, or in a retrograde direction.

Almost all of the orbits in the Solar System are caused by the initial collapse of the Solar System 4.6 billion years ago from the solar nebula. As the cloud of gas and dust collapsed down into the stellar disk, the conservation of angular momentum caused the disk to rotate. The Sun formed out of a bulge in the center of the Solar System, and the planets formed out of lumps in the protoplanetary disk.

And so, all of the planets in the Solar System orbit in a prograde direction. And then the planets themselves also collapsed down, and started rotating because of the conservation of angular momentum. And again, almost all of the planets rotate in a prograde direction; except one: Venus. When seen from above their north pole, all the planets rotate in a counter-clockwise direction. But Venus is actually rotating in a clockwise direction.

It’s believed that most of the moons in the Solar System formed in place around their planets. And so they orbit in a prograde direction as well, orbiting in the same direction that their planet turns. There are a few exceptions; however, like Neptune’s moon Titan, which orbits in a retrograde direction.

Because the Earth and the planets are orbiting the Sun, we get a changing perspective of their position as we go around the Sun. The planets can seem to slow down, stop, and then move backwards in the sky. Of course, they’re not actually going backwards in their orbit, but we’re seeing that from our perspective. When the planets move in this backwards direction, they’re said to be “in retrograde”. And then they start moving forward again and come out of retrograde.

We’ve written a few articles about retrograde orbits for Universe Today. Here’s an article about Mercury in retrograde, the 2009 Mercury retrograde dates, and here’s an article about Venus in retrograde.

If you’d like more information on orbits, check out this cool list of orbit diagrams. And here’s more info on Neptune’s moon Triton, which follows a retrograde orbit.

We’ve also done an episode of Astronomy Cast about Neptune. Listen here, Episode 63: Neptune.