Time Magazine Top 10 Scientific Discoveries of 2008: Space and Physics Dominate

Direct observation of an exoplanet orbiting the star Fomalhaut - Number 6 in the top 10 (NASA/HST)

[/caption]2008 has been an astounding year of scientific discovery. To celebrate this fact, Time Magazine has listed the “Top 10 Scientific Discoveries” where space exploration and physics dominate. Other disciplines are also listed; including zoology, microbiology, technology and biochemistry, but the number 1 slot goes to the most ambitious physics experiment of our time. Can you guess what it is? Also, of all our endeavours in space, can you pick out three that Time Magazine has singled out as being the most important?

As we approach the end of the year, ready to welcome in 2009, it is good to take stock and celebrate the mind-blowing achievements mankind has accomplished. Read on for the top 10 scientific discoveries of 2008

The best thing about writing for a leading space news blog is that you gain wonderful overview to all our endeavours in astronomy, space flight, physics, politics (yes, space exploration has everything to do with politics), space commercialization and science in general. 2008 has been such a rich year for space exploration; we’ve landed probes on other worlds, studied other worlds orbiting distant stars, peered deep into the quantum world, learnt profound things about our own planet, developed cutting-edge instrumentation and redefined the human existence in the cosmos. We might not have all the answers (in fact, I think we are only just beginning to scratch the surface of our understanding of the Universe), but we have embarked on an enlightening journey on which we hope to build strong foundations for the next year of scientific discovery.

In an effort to assemble some of the most profound scientific endeavours of this year, Time Magazine has somehow narrowed the focus down to just 10 discoveries. Out of the ten, four are space and physics related, so here they are:

6. Brave New Worlds: First direct observations of exoplanets

Infrared observations of a multi-exoplanet star system HR 8799 (Keck Observatory)
Infrared observations of a multi-exoplanet star system HR 8799 (Keck Observatory)
In November, we saw a flood of images of alien worlds orbiting distant stars. On the same day, Hubble publicised strikingly sharp images of an exoplanet orbiting a star called Fomalhaut (pictured top) and then a ground-based Keck-Gemini campaign made the first direct observations of a multi-exoplanet system around a star called HR8799 (pictured left). A few days later, yet another image came in from another research group at the European Southern Observatory, spotting the very compact orbit of an exoplanet around the star Beta Pictorus.

Considering there have never been any direct observations of exoplanets before November 2008–although we have known about the presence of worlds orbiting other stars for many years via indirect methods–this has been a revolutionary year for exoplanet hunters.

4. China Soars into Space: First taikonaut carries out successful spacewalk

Zhai Zhigang exits the Shenzhou-7 capsule with Earth overhead (Xinhua/BBC)
Zhai Zhigang exits the Shenzhou-7 capsule with Earth overhead (Xinhua/BBC)
Following hot on the heels of one of the biggest Olympic Games in Beijing, China launched a three-man crew into space to make history. The taikonauts inside Shenzhou-7 were blasted into space by a Long March II-F rocket on September 25th.

Despite early controversy surrounding recorded spaceship transmissions before the rocket had even launched, and then the sustained efforts by conspiracy theorists to convince the world that the whole thing was staged, mission commander Zhai Zhigang did indeed become the first ever Chinese citizen to carry out a spacewalk. Zhai spent 16 minutes outside of the capsule, attached by an umbilical cable, to triumphantly wave the Chinese flag and retrieve a test sample of solid lubricant attached to the outside of the module. His crew mate Liu Boming was also able to do some spacewalking.

Probably the most incredible thing about the first Chinese spacewalk wasn’t necessarily the spacewalk itself, it was the speed at which China managed to achieve this goal in such a short space of time. The first one-man mission into space was in 2003, the second in 2005, and the third was this year. Getting man into space is no easy task, to build an entire manned program in such a short space of time, from the ground-up, is an outstanding achievement.

2. The North Pole – of Mars: The Phoenix Mars Lander

Phoenix (NASA/UA)
Capturing the world's attention: Phoenix (NASA/UA)
Phoenix studied the surface of the Red Planet for five months. It was intended to only last for three. In that time, this robotic explorer captured the hearts and minds of the world; everybody seemed to be talking about the daily trials and tribulations of this highly successful mission. Perhaps it was because of the constant news updates via the University of Arizona website, or the rapid micro-blogging via Twitter; whatever the reason, Phoenix was a short-lived space celebrity.

During the few weeks on Mars, Phoenix discovered water, studied atmospheric phenomena, plus it characterized the regolith to find it is more “soil-like” than we gave it credit for. However, Phoenix also discovered a chemical called perchlorate that could be hazardous to life on the Martian surface, but there is a flip-side to that coin; the chemical may provide energy for basic forms of life.

Like all good adventures there were twists and turns in Phoenix’s progress, with the odd conspiracy thrown in for good measure. Even during Phoenix’s sad, slow death, the lander had some surprises in store before it slowly slipped into a Sun-deprived, low energy coma.

To give the highly communicative lander the last word, MarsPhoenix on Twitter has recently announced: “Look who made Time Mag’s Top 10 list for Scientific Discoveries in 2008: http://tinyurl.com/5mwt2l

1. Large Hadron Collider

The complexity of the Large Hadron Collider (CERN/LHC/GridPP)
The complexity of the Large Hadron Collider (CERN/LHC/GridPP)

Speaking of “capturing the hearts and minds” of the world, the Large Hadron Collider (LHC) has done just that, but not always in a positive way (although common sense seems to be winning). So, in the #1 spot of Time Magazine’s Top 10 Scientific Discoveries of 2008, the LHC is a clear winner.

In the run-up to the switch-on of the LHC in September, the world’s media focused its attention on the grandest physics experiment ever constructed. The LHC will ultimately probe deep into the world of subatomic particles to help to explain some of the fundamental questions of our Universe. Primarily, the LHC has been designed to hunt for the elusive Higgs boson, but the quest will influence many facets of science. From designing an ultra-fast method of data transmission to unfolding the theoretical microscopic dimensions curled up in space-time, the LHC is a diverse science, with applications we won’t fully appreciate for many years.

Unfortunately, as you may be wondering, the LHC hasn’t actually discovered anything yet, but the high-energy collisions of protons and other, larger subatomic particles, will revolutionize physics. I’d argue that the simple fact the multi-billion euro machine has been built is a discovery of how advanced our technological ability is becoming.

Although the first particles were circulated on that historic day on September 10th, we’ll have to wait for the first particle collisions to occur some time in the summer of 2009. Engineers are currently working hard to repair the estimated £14 million (~$20 million) damage caused by the “quench” that knocked out a number of superconducting electromagnets on September 19th.

For more, check out the Top 10 Scientific Discoveries in Time Magazine, there’s another six that aren’t related to space or physics

Venus and Mercury

Saturn, Venus and Mercury. Image credit: Jimmy Westlake

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Venus and Mercury are the two planets that orbit closest to the Sun. Mercury orbits at an average distance of 58 million km, while Venus orbits at a distance of 108 million km. Mercury takes 88 Earth days to complete an orbit, and Venus takes 225 days to orbit the Earth.

And as you’d probably guess, Venus and Mercury are the two hottest planets in the Solar System, but not in the order that you’d think. Even though Mercury orbits closer to the Sun than Venus, it lacks an atmosphere. The side facing the Sun is baked, with a temperature of 425 degrees Celsius, the side facing away from the Sun cools down to -193 degrees Celsius. Venus, on the other hand, has an incredibly thick atmosphere and traps the heat from the Sun. No matter where you go on the planet, the temperature on the surface of Venus is always 462 degrees Celsius.

The composition of Venus and Mercury is similar, they’re both terrestrial planets made of rock and metal. Mercury is more dense than Venus and thought to consist of 60-70% metal, with the rest rock. As mentioned above, Mercury lacks an atmosphere, while Venus has the thickest atmosphere of all the terrestrial planets. The temperatures and pressures are so extreme on the surface of Venus that spacecraft only last a few hours before being crushed and baked.

Both Venus and Mercury are within the orbit of Earth. This means that they’re always located near the Sun in the sky. Sometimes they rise before the Sun, and then fade away as the Sun rises, and sometimes they’re set after the Sun. They appear as the sky darkens, and then pass below the horizon within a few minutes. You need to have a clear view to the horizon to see Mercury, and know when to go looking. Venus, on the other hand can appear quite high in the sky, and is very bright. In fact, Venus is the brightest object in the sky after the Moon.

We have written many articles about both Venus and Mercury on Universe Today. Here’s an article about new images captured of Mercury by NASA’s MESSENGER spacecraft. And here’s an article about a potential way to colonize Venus.

If you’d like more information on Mercury, check out NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Misson Page.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

Venus y Mercurio

References:
NASA Solar System Exploration: Venus
NASA Solar System Exploration: Mercury

Mercury Retrograde

Retrograde motion of Mars. Image credit: NASA

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Ancient people have known about the planets since we were able to look up. Some stars were brighter than the rest, and seemed to move across the sky from night to night. These moving stars were known as planets, and there were 5: Mercury, Venus, Mars, Jupiter and Saturn. But the movements of the planets were puzzling to ancient astronomers. Some times the planets would slow down, go backwards, and then go forwards again. When a planet goes backwards, it’s called retrograde, and one of the best planets for this is Mercury. Let’s examine Mercury retrograde.

In ancient times, people thought the Earth was the center of the Universe, and all objects in the night sky orbited around us. One complication of this model was the planets which took these very predictable retrograde paths in their orbit. If the planets were orbiting the Earth, why would they go backwards? Why would Mercury go retrograde? They developed elaborate models where the planets followed a spiraling path around the Earth to account for this retrograde motion.

It wasn’t until Nicolaus Copernicus developed his Sun-centered model of the Solar System that the bizarre retrograde motion of Mercury and the rest of the planets finally made sense. The Earth is just another planet, and they’re all orbiting the Sun together. The retrograde motion of Mercury and the other planets is due to our relative positions in orbit.

So let’s understand retrograde motion, and look at what is Mercury retro in particular. The motion of the planets around the Sun follow the right-hand rule. Hold your right hand out, make a fist and stick the thumb up. The direction of the thumb points in the direction of the Sun’s northern pole. The curve of the fingers indicates the direction all the planets orbit around the Sun.

Mercury moves faster than the Earth as it travels around the Sun; however, Mercury has a highly elliptical orbit, so the speed of its orbit changes. When Mercury is furthest from the Sun, it’s at the slowest point in its orbit, and this gives the Earth a chance to “catch up”. Imagine you’re driving next to a car in the freeway which is speeding up and slowing down. It’s still going down the highway at a high speed, but it seems to be going back and forth compared to you. When this happens, astronomers say that Mercury is in retrograde.

Astrologers seem to think that retrograde motion is an unlucky or bad situation because it goes against a planet’s natural movements. Of course, the planet isn’t really changing its motions at all, it’s only our perspective of the planet that’s changing. Furthermore, at any one time, 40% of the outer planets are in retrograde motion anyway. Something’s almost always in retrograde.

Is Mercury in retrograde right now? It depends on the date. Check the list of dates below to check.

So when is Mercury going to be in retrograde? Here are some Mercury retrograde dates for the next few years.

Mercury Retrograde 2009

  • January 11-31
  • May 6-20
  • September 6-29
  • December 26-January 15, 2010

Mercury Retrograde 2010

  • April 17-May 11
  • August 20 – September 12
  • December 10-December 29

Mercury Retrograde 2011

  • March 30-April 23
  • August 2 – August 26
  • November 23 – December 13

Mercury Retrograde 2012

  • March 11-April 4
  • July 14 – August 7
  • November 6 – November 26

Here’s a link to the 2009 mercury retrograde dates.

If you’d like more information on Mercury, check out NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Misson Page.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

Mercurio retrógrada

References:
NASA: Planetary Motion
NASA Astronomy Picture of the Day
NASA: Mercury

Beyond Any Reasonable Doubt: A Supermassive Black Hole Lives in Centre of Our Galaxy

The stars in the centre of our galaxy. Our supermassive black hole IS in there, somewhere... (ESO)

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One the one hand, this might not be surprising news, but on the other, the implications are startling. A supermassive black hole (called Sagittarius A*) lives at the centre of the Milky Way. This is the conclusion of a 16 year observation campaign of a region right in the centre of our galaxy where 28 stars have been tracked, orbiting a common, invisible point.

Usually these stars would be obscured by the gas and dust in that region, but the European Southern Observatory (ESO) in Chile has used its infrared telescopes to peer deep into the black hole’s lair. Judging by the orbital trajectories of these 28 stars, astronomers have not only been able to pinpoint the black hole’s location, they have also deduced its mass…

It has been long recognised that supermassive black holes probably occupy the centres of most galaxies, from dwarf galaxies to thin galactic disks to large spiral galaxies; the majority of galaxies appear to have them. But actually seeing a black hole is no easy task; astronomers depend on observing the effect a supermassive black hole has on the surrounding gas, dust and stars rather than seeing the object itself (after all, by definition, a black hole is black).

Yearly location of stars within 0.2 parsecs from Sagittarius A* orbiting the common, compact radio source (from a different research paper by A. Ghez)In 1992, astronomers using the ESO’s 3.5-metre New Technology Telescope in Chile turned their attentions on our very own galactic core to begin an unprecedented observation campaign. Since 2002, the 8.2-metre Very Large Telescope (VLT) was also put to use. 16 years later, with over 50 nights of total observation time, the results are in.

By tracking individual stars orbiting a common point, ESO researchers have derived the best empirical evidence yet for the existence of a 4 million solar mass black hole. All the stars are moving rapidly, one star even completed a full orbit within those 16 years, allowing astronomers to indirectly study the mysterious beast driving our galaxy.

The centre of the Galaxy is a unique laboratory where we can study the fundamental processes of strong gravity, stellar dynamics and star formation that are of great relevance to all other galactic nuclei, with a level of detail that will never be possible beyond our Galaxy,” explains Reinhard Genzel, team leader of this research at the Max-Planck-Institute for Extraterrestrial Physics in Garching near Munich, Germany.

Undoubtedly the most spectacular aspect of our 16-year study, is that it has delivered what is now considered to be the best empirical evidence that super-massive black holes do really exist,” Genzel continues. “The stellar orbits in the galactic centre show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt.”

Apart from being the most detailed study of Sagittarius A*’s neighbourhood (the techniques used in this study are six-times more precise than any study before it), the ESO astronomers also deduced the most precise measurement of the distance from the galactic centre to the Solar System; our supermassive black hole lies a safe 27,000 light years away.

A lot of information was gleaned about the individual stars too. “The stars in the innermost region are in random orbits, like a swarm of bees,” says Stefan Gillessen, first author of the paper published in The Astrophysical Journal. “However, further out, six of the 28 stars orbit the black hole in a disc. In this respect the new study has also confirmed explicitly earlier work in which the disc had been found, but only in a statistical sense. Ordered motion outside the central light-month, randomly oriented orbits inside – that’s how the dynamics of the young stars in the Galactic Centre are best described.”

Quite simply, the object influencing these stars must be a supermassive black hole, there is no other explanation out there. Does this mean black holes have an even firmer standing as a cosmological “fact” rather than “theory”? It would appear so

Sources: ESO, BBC

Life on Mercury

How hot is it on Mercury? Color image of Mercury. Image credit: NASA

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Mercurian world is one of extremes. 700 Kelvin on the side exposed to the Sun, yet some areas are never exposed to sunlight and are as cold as deep space. Scientists do not believe there has ever been life on Mercury. The atmosphere on Mercury is almost non-existant. It doesn’t protect the planet from the harsh radiation of the Sun or radiation from space, nor does it trap heat and provide a breathable atmosphere. Mercury is inhospitable and sterile.

In order for life (as we know it) to exist, Mercury would need to have temperatures that allow liquid water to remain on its surface for long periods of time. But the temperatures on Mercury extend from just above absolute zero when the surface is shadowed to 700 Kelvin when its in sunlight. Liquid water just can’t exist in that kind of environment.

Any ancient life on Mercury would have faced many extinction events. Here on Earth many past life forms have been destroyed by asteroid impacts. The dinosaurs are a classic example. Images of Mercury’s surface returned by the Mariner 10 and MESSENGER spacecraft have shown that the surface has suffered many large impacts. In fact, it was heavily bombarded during the Late Heavy Bombardment that occurred about 3.9 billion years ago. Any one of those impacts could have destroyed any life on the planet. Many scientists believe that a great deal of the planet’s surface was stripped away by one impact. If the impact removed a large portion of the surface, surely it would have taken any life that existed at the time with it.

All evidence that science has do date indicates that there has never been life on Mercury and never will be. The harsh conditions on the planet’s surface and the tenuous atmosphere make it impossible for any life form known to man to exist.

But there are other planets in the Solar System. Here’s an article about life on Pluto, and here’s one about life on Mars.

If you’d like more information on Mercury, check out NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Misson Page.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

Vida sobre el mercurio

References:
NASA Solar System Exploration: Mercury
Wikipedia
JAXA: Mercury Quantities
NASA MESSENGER Mission
NASA Multimedia

Pluto and Neptune

Neptune from Voyager 2. Image credit: NASA/JPL

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The most distant planet in the Solar System is Neptune, orbiting at a distance of 4.5 billion km from the Sun. But there used to be 9 planets in the Solar System, including Pluto. And for most of the time since its discovery, Pluto was considered the most distant planet from the Sun.

Pluto and Neptune couldn’t be more different. Pluto is a tiny Kuiper Belt Object; a ball of rock and ice measuring only 2,390 km across. This is a tiny fraction of the diameter of Neptune, which is 49,500 km across. You could fit 20 Plutos side by side to match the diameter of Neptune.

Neptune and Pluto have a very interesting orbital dynamic between them. Neptune has a roughly circular orbit; however, Pluto’s orbit is highly eccentric, varying its distance to the Sun a tremendous amount over the course of its orbit. Because of this, Pluto can actually get closer to the Sun than Neptune. The last time this happened started in 1979 and went until 1999. During that period, Neptune was actually the most distant planet from the Sun, and Pluto was actually closer. But then Pluto was demoted, from planet to dwarf planet, so Neptune is now the most distant planet; and it doesn’t matter what Pluto does. Pluto spends 20 years out of its entire 248 year orbit within Neptune’s orbit.

Since Pluto and Neptune cross orbits, is it possible that the two planets will collide? No, they actually can’t collide because Pluto’s orbit takes it much higher above the Sun’s orbital plane. When Pluto is at the same point as Neptune’s orbit, it actually much higher up than Neptune. So the two planets will never be at the same place at the same time.

You can read some interesting information about the orbital patterns of Pluto here.

We have written many articles about Pluto and Neptune on Universe Today. Here’s why Pluto is no longer considered a planet, and here’s an article about how there could be liquid oceans inside 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.

Source: NASA

What is the Weather Like on Neptune?

Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL

Neptune is the most distant planet from the Sun, with temperatures that plunge down to 55 Kelvin, or -218 degrees Celsius. You would think that a planet that cold would be frozen and locked down, with very little weather. But you’d be very wrong. In fact, the weather on Neptune is some of the most violent weather in the Solar System.

Just like Jupiter and Saturn, Neptune has bands of storms that circle the planet. While the wind speeds on Jupiter can reach 550 km/hour – twice the speed of powerful hurricanes on Earth, that’s nothing compared to Neptune. Astronomers have clocked winds on Neptune traveling at 2,100 km/hour.

So why can the winds on Neptune reach such huge speeds? Astronomers think that the cold temperatures on Neptune might have something to do with that after all. The cold temperatures might decrease the friction in the system, so that winds can get going fast on Neptune.

During its 1989 flyby, NASA’s Voyager 2 spacecraft discovered the Great Dark Spot on Neptune. Similar to Jupiter’s Great Red Spot, this is an anti-cyclonic storm measuring 13,000 km x 6,600 km across. A few years later, however, the Hubble Space Telescope failed to see the Great Dark Spot, but it did see different storms. This might mean that storms on Neptune don’t last as long as they do on Jupiter or even Saturn.

The more active weather on Neptune might be due, in part, to its higher internal heat. Although Neptune is much more distant than Uranus from the Sun, receiving 40% less sunlight, temperatures on the surface of the two planets are roughly similar. In fact, Neptune radiates 2.61 times as much energy as it receives from the Sun. This is enough heat to help drive the fastest winds in the Solar System.

We have written many articles about Neptune for Universe Today. Here’s an article about how Neptune’s south pole is the warmest part of the planet, and here’s more information about the atmosphere on 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.

Neptune Compared to Earth

Neptune compared to Earth. Image credit: NASA

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To really understand how big Neptune really is, you need some kind of comparison. Let’s see how Neptune compares to Earth in every way.

First, let’s just look at pure size. The diameter of Neptune is approximately 49,500 km. This makes Neptune the 4th largest planet in the Solar System. And compared to Earth? Neptune is 3.9 times bigger.

Now mass. The mass of Neptune is 1.02 x 1026 kg. If you wanted to write it out, it would be 102,000,000,000,000,000,000,000,000 kg. Neptune has 17 times as much mass compared to the Earth.

How about volume? The volume of Neptune is 6.3 x 1013 km3. You could fit 57 Earths inside Neptune and still have room to spare.

A day on Earth is 24 hours, but a day on Neptune is 16 hours and 6 minutes. A year on Earth is, um, 1 year obviously, while a year on Neptune is 164.79 years.

Here’s one element that’s actually pretty close. The surface gravity on Neptune (if it actually had a surface that you could stand on) is only 14% stronger than the pull of gravity on Earth. You would have a difficult time noticing if you were standing on the surface of Neptune compared to the surface of Earth.

We have written many articles about Neptune for Universe Today. Here’s an article about three new trojan asteroids found in Neptune’s orbit, and a possible mission to Neptune under study.

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.

Neptune’s Orbit

Neptune seen from Earth. Image credit: Keck

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Neptune orbits the Sun at an average distance of 4.5 billion km.

That’s the simple answer to the question, what is the orbit of Neptune. However, things are actually a little more complicated than that. Like all the planets in the Solar System, Neptune follows an elliptical path around the Sun, varying its distance to the Sun at different points along its orbit.

At its closest point in its orbit, which astronomers call perihelion, Neptune gets within 4.45 billion km, or 29.77 astronomical units (1 astronomical unit or AU is the average distance of the Earth to the Sun).

At its most distant point in its orbit, called aphelion, Neptune reaches a distance of 4.55 billion km, or 30.44 astronomical units.

One interesting feature about the orbit of Neptune is the fact that Pluto’s very elliptical orbit sometimes brings it closer to the Sun. Back in the days when Pluto was still a planet, it would spend a few decades every orbit closer to the Sun. So Neptune was actually the most distant planet, and Pluto was closer. The last time this happened started in 1979, and ended in 1999. Of course, Pluto isn’t a planet any more, so Neptune’s orbit makes it the most distant planet.

We have written many article about Neptune on Universe Today. Here’s an article with images of Neptune captured by the Hubble Space Telescope. And here’s another discussing the planet’s relatively warm south pole.

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.

Radius of Neptune

Neptune compared to Earth. Image credit: NASA

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The equatorial radius of Neptune is 24,764 km.

That’s the quick answer. But you need to understand that things are a little more complicated. Like all of the planets in the Solar System, Neptune is spinning rapidly, completing a rotation in 16 hours and 6 minutes. This rapid rotation causes the planet to flatten out, so that the radius across the equator is bigger than the radius to the poles.

So here’s the more precise answer. The radius of Neptune, measured from the center to the equator is 24,764 km. And the radius of Neptune, measured from the center to either pole is 24,341 km. I’ll do the math for you. That means that the points on the equator are 423 km further away from the center of Neptune than either pole.

Need some comparison? Neptune’s radius is 3.9 times the radius of Earth. In other words, you could line up almost 4 Earths side by side to match the width of Neptune.

We have written many articles about Neptune for Universe Today. Here’s an article about the potential for liquid water deep down within Neptune. And here’s an article about how Neptune’s largest moon Triton might have been captured by Neptune’s gravity.

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.