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Dwarf Planet Makemake Lacks Atmosphere

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Distant frigid world reveals its secrets for the first time

Artist’s impression of the surface of the dwarf planet Makemake

Astronomers have used three telescopes at ESO’s observatories in Chile to observe the dwarf planet Makemake as it drifted in front of a distant star and blocked its light. The new observations have allowed them to check for the first time whether Makemake is surrounded by an atmosphere. This chilly world has an orbit lying in the outer Solar System and was expected to have an atmosphere like Pluto (eso0908), but this is now shown not to be the case. The scientists also measured Makemake’s density for the first time. The new results are to be published in the 22 November issue of the journal Nature.

Dwarf planet Makemake [1] is about two thirds of the size of Pluto, and travels around the Sun in a distant path that lies beyond that of Pluto but closer to the Sun than Eris, the most massive known dwarf planet in the Solar System (eso1142). Previous observations of chilly Makemake have shown it to be similar to its fellow dwarf planets, leading some astronomers to expect its atmosphere, if present, to be similar to that of Pluto. However, the new study now shows that, like Eris, Makemake is not surrounded by a significant atmosphere.

The team, led by José Luis Ortiz (Instituto de Astrofísica de Andalucía, CSIC, Spain), combined multiple observations using three telescopes at ESO’s La Silla and Paranal observing sites in Chile — the Very Large Telescope (VLT), New Technology Telescope (NTT), and TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) — with data from other small telescopes in South America [2], to look at Makemake as it passed in front of a distant star [3].

“As Makemake passed in front of the star and blocked it out, the star disappeared and reappeared very abruptly, rather than fading and brightening gradually. This means that the little dwarf planet has no significant atmosphere,” says José Luis Ortiz. “It was thought that Makemake had a good chance of having developed an atmosphere — that it has no sign of one at all shows just how much we have yet to learn about these mysterious bodies. Finding out about Makemake’s properties for the first time is a big step forward in our study of the select club of icy dwarf planets.”

Makemake’s lack of moons and its great distance from us make it difficult to study [4], and what little we do know about the body is only approximate. The team’s new observations add much more detail to our view of Makemake — determining its size more accurately, putting constraints on a possible atmosphere and estimating the dwarf planet’s density for the first time. They have also allowed the astronomers to measure how much of the Sun’s light Makemake’s surface reflects — its albedo [5]. Makemake’s albedo, at about 0.77, is comparable to that of dirty snow, higher than that of Pluto, but lower than that of Eris.

It was only possible to observe Makemake in such detail because it passed in front of a star — an event known as a stellar occultation. These rare opportunities are allowing astronomers for the first time to find out a great deal about the sometimes tenuous and delicate atmospheres around these distant, but important, members of the Solar System, and providing very accurate information about their other properties.

Occultations are particularly uncommon in the case of Makemake, because it moves in an area of the sky with relatively few stars. Accurately predicting and detecting these rare events is extremely difficult and the successful observation by a coordinated observing team, scattered at many sites across South America, ranks as a major achievement.

“Pluto, Eris and Makemake are among the larger examples of the numerous icy bodies orbiting far away from our Sun,” says José Luis Ortiz. “Our new observations have greatly improved our knowledge of one of the biggest, Makemake — we will be able to use this information as we explore the intriguing objects in this region of space further.”

Notes
[1] Makemake was initially known as 2005 FY9. It was discovered a few days after Easter in March 2005, earning it the informal nickname of Easterbunny. In July 2008 it was given the official name of Makemake. Makemake is the creator of humanity and god of fertility in the myths of the native people of Easter Island.

Makemake is one of five dwarf planets so far recognised by the International Astronomical Union. The others are Ceres, Pluto, Haumea and Eris. Further information about dwarf planets and planets is available from the International Astronomical Union.

[2] Another of the telescopes used in this observing campaign was an 0.84-metre telescope installed by the Católica del Norte University of Chile. This telescope is sited on Cerro Armazones, the future site of the European Extremely Large Telescope (E-ELT).

[3] Makemake passed in front of faint star NOMAD 1181-0235723 (where NOMAD refers to the Naval Observatory Merged Astrometric Dataset) on 23 April 2011. The team observed this event using seven different telescopes across Brazil and Chile. The event only lasted about one minute, so the astronomers took advantage of a specialised high-speed camera known as ULTRACAM (eso0520) and a high-speed infrared imager named ISAAC to capture the event.

[4] In the case of objects that are orbited by one or more moons the motions of the moons can be used to deduce the mass of the object. This was not possible in the case of Makemake.

[5] The dwarf planet was calculated to have a geometrical albedo of 0.77 ± 0.03, greater than Pluto’s, but smaller than that of Eris. An albedo of 1 represents a perfectly reflecting body, and 0 a black surface that does not reflect at all. The observations, together with previous results, indicate that Makemake has a density of 1.7 ± 0.3 grams per cubic centimetre, which in turn allowed the team to infer the shape and appearance of an oblate spheroid — a sphere flattened slightly at both poles — with axes of 1430 ± 9 kilometres and 1502 ± 45 kilometres. Makemake shows no global Pluto-like atmosphere at a level of one thousandth of that of Pluto’s atmosphere. However, it may have an atmosphere that only covers part of the surface. Such a local atmosphere, which is possible in theory, is not excluded by the observations.
Read more: www.eso.org

Written by physicsgg

November 21, 2012 at 8:22 pm

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Star is caught devouring planet

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First Evidence Discovered of Planet’s Destruction by Its Star

The first evidence of a planet’s destruction by its aging star indicates that the missing planet was devoured as the star began expanding into a “red giant” — the stellar equivalent of advanced age. “A similar fate may await the inner planets in our solar system, when the Sun becomes a red giant and expands all the way out to Earth’s orbit some five-billion years from now,” said Alexander Wolszczan, Evan Pugh Professor of Astronomy and Astrophysics at Penn State and the discoverer of the first planet ever found outside our solar system. (Credit: Marty Harris/McDonald Obs./UT-Austin)

The first evidence of a planet’s destruction by its aging star has been discovered by an international team of astronomers. The evidence indicates that the missing planet was devoured as the star began expanding into a “red giant” — the stellar equivalent of advanced age…
Read more: sciencedaily.com

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August 21, 2012 at 1:37 pm

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The Milky Way’s 100 Billion Planets

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This artist’s illustration gives an impression of how common planets are around the stars in the Milky Way. The planets, their orbits and their host stars are all vastly magnified compared to their real separations. A six-year search that surveyed millions of stars using the microlensing technique concluded that planets around stars are the rule rather than the exception. The average number of planets per star is greater than one. This means that there is likely to be a minimum of 1,500 planets within just 50 light-years of Earth.

The results are based on observations taken over six years by the PLANET (Probing Lensing Anomalies NETwork) collaboration, which was founded in 1995. The study concludes that there are far more Earth-sized planets than bloated Jupiter-sized worlds. This is based on calibrating a planetary mass function that shows the number of planets increases for lower mass worlds. A rough estimate from this survey would point to the existence of more than 10 billion terrestrial planets across our galaxy.

The results were published in the Jan. 12, 2012, issue of the British science journal Nature.
Image Credit: NASA, ESA, and M. Kornmesser (ESO)
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Written by physicsgg

April 26, 2012 at 12:21 pm

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New model provides different take on planetary accretion

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This image of the Eagle Nebula, made with data from the Kitt Peak telescope, corresponds more closely to the authors’ model than to the traditional model. In their model planets form in a cold, three-dimensional cloud of gas and dust.

By Tony Fitzpatrick
The prevailing model for planetary accretion, also called fractal assembly, and dating back as far as the 18th century, assumes that the Solar System’s planets grew as small grains colliding chaotically, coalescing into bigger ones, colliding yet more until they formed planetesimals. The planetesimals then collided until they formed planets as varied as the Earth and Jupiter.

The model assumes that this occurred in an extremely hot (as high as 1,600 degrees Celsius) environment for the inner Solar System, fostered by a dusty, two-dimensional disk post-dating the Sun.

The basic modern model, developed by Russian astronomer Victor Safronov, and further developed by planetary scientist George Wetherill, is called the Solar Nebular Disk Model and was made available in English in the early 1970s. It has remained essentially the same over the past 40 years.

But not everyone is convinced the model is correct. How could such a chaotic, haphazard process as fractal assembly lead to the regularities of the Solar System with all of the planets in a single plane, rotating in the same sense, spinning and orbiting around the Sun?

For the discontents, a new model, offered by Anne Hofmeister, PhD, research professor of earth and planetary sciences and Robert Criss, PhD, professor in earth and planetary sciences at Washington University in St. Louis, presents a different scenario. Their explanation is published in the March issue ofPlanetary and Space Science.

Using classical physics, the laws of thermodynamics and mechanics, Hofmeister, with assistance from Criss, presents an accretion model that assumes a three-dimensional (3-D) gas cloud. This pre-solar nebula collapses and forms the Sun and planets at essentially the same time, with the planets contracting toward the Sun.

The temperature is cold, not hot. The thermodynamic and mechanical model of 3-D accretion explains planetary orbits and spins, unlike the 2-D model, which does not.

Hofmeister and Criss explain compositional gradients across the Solar System in terms of lighter molecules diffusing faster than heavier ones. The model connects planet mass to satellite system size via gravitational competition.

Explaining planetary orbits and spins

“This model is radically different,” Hofmeister says. “I looked at the assumption of whether heat could be generated when the nebula contracted and found that there is too much rotational energy in the inner planets to allow energy to spill into heating the nebula.

“Existing models for planetary accretion assume that the planets form from the dusty 2-D disk, but they don’t conserve angular momentum. It seemed obvious to me to start with a 3-D cloud of gas, and conserve angular momentum. The key equations in the paper deal with converting gravitational potential to rotational energy, coupled with conservation of angular momentum.”

No energy left over for heat

“In the new model, heat production is not important in planetary formation,” Hofmeister says.

Criss says the prevailing notion that gravitational collapse is a hot process is a mis-interpretation of thermodynamics. He offers an analogy of a beaker of water placed outside in the winter. It slowly starts to freeze. Freezing water actually releases a latent heat, he says, because order (ice, a crystal) is being made from disorder (liquid).

The heat released is considerable, but it cannot warm the beaker because “it’s released only as fast as the environment will take it away,” Criss says. “If the heat would warm the water above 32 degrees Fahrenheit, the ice would melt. People clinging to the old accretion models want to make the ice and heat the beaker, too.”

Gravitational competition

The authors say 2-D models don’t explain why the inner Solar System is comprised of rocky planets and the outer gas giants.

“The first thing that happens in planet accretion is forming rocky kernels,” Hofmeister says. “The nebula starts contracting, the rocky kernels form to conserve angular momentum, and that’s where the dust ends up. Once rocky kernels exist, they attract gas to them, but only if the rocky kernel is far from the Sun, can it out-compete the Sun’s gravitational pull and collect the gas, as did Jupiter and its friends.

“But if the rocky kernel is close, like the Earth’s, it can’t out-compete the Sun. We describe this process as gravitational competition. This is why we have the regularity, spacing, and graded composition of the Solar System.”

Gravitational competition also offers a new view of formation of the moon that does not require an extremely low probability giant impact.

Not limited to the Solar System

Hofmeister says there is a continuum between single stars, binary stars, multiple stars, planets and even extrasolar planets.

“In all cases, the process is gravitational accretion of these cold, 3-D clouds making things contract and spin out, and that’s where the energy comes from,” she says. “It’s all happening in very cold temperatures, in 3-D instead of 2-D.”

Criss says there is plenty of observable evidence that the 2-D model is wrong.

“It patently doesn’t make sense that a bunch of random collisions between heavy, solid objects are going to produce a Solar System with planets orbiting the Sun in a beautiful plane, with everything having upright spins,” he says. “That’s like setting off a nuclear bomb and expecting all the trees in the world to end up neatly stacked.

Moreover, the Hubble pictures show stars being born in the Eagle nebula, and they’re formed in a cold 3-D cloud.”…

Read more: http://news.wustl.edu/news/Pages/23466.aspx

Written by physicsgg

March 3, 2012 at 9:00 pm

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New planet, the youngest ever found

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…is revealed by cosmic trick photography

US and Australian astronomers cancel out light from solar cloud to reveal new planet LkCa 15 b forming in swirl of stardust

Left, the shining dust and gas cloud around the star LkCa 15. Right, an expanded view of the central region, showing the forming planet and the position of the central star

A University of Hawaii astronomer has captured the first direct image of a planet forming around a star. Dubbed LkCa 15 b, it is the youngest planet ever found.

The university’s Institute for Astronomy said Adam Kraus used telescopes on Mauna Kea island to find the planet. He was working with Michael Ireland from Macquarie University and the Australian Astronomical Observatory.

Artist’s conception of the view near the planet LkCa 15 b

LkCa 15 b is 450 light years away from Earth and being built by dust and gas.

Scientists had not been able to see such young planets before because their parent solar systems’ light outshines them.

Krause and Ireland used mirrors to cancel out the starlight and were able to see discs of dust near the planet.

The astronomers used 10-metre Keck telescopes to reveal the forming planet sitting inside a wide gap between the young parent star and the outer disc of glowing dust.
“LkCa 15 b is the youngest planet ever found, about five times younger than the previous record holder,” Kraus said. “This young gas giant is being built out of the dust and gas. In the past you couldn’t measure this kind of phenomenon because it’s happening so close to the star. But for the first time we’ve been able to directly measure the planet itself as well as the dusty matter around it.”

Kraus presented the discovery at Nasa’s Goddard Space Flight Centre on Wednesday after his research paper on the discovery with Ireland was accepted by the Astrophysical Journal.

The optical sleight of hand used by the astronomers combined the telescope’s “adaptive optics” with a technique called aperture mask interferometry: using a a deformable mirror to rapidly correct for atmospheric distortions to starlight. It involves placing a small mask with several holes in the path of the light collected and concentrated by a giant telescope, and using it to manipulate the light waves.
“It’s like we have an array of small mirrors,” Kraus said. “We can manipulate the light and cancel out distortions.” The technique allows the astronomers to remove the bright light of stars. They can then resolve discs of dust around stars and see gaps in the dusty layers where protoplanets may be hiding.

“We realised we had uncovered a super Jupiter-sized gas planet but that we could also measure the dust and gas surrounding it. We’d found a planet, perhaps even a future solar system at its very beginning.”
Kraus and Ireland plan to continue their planet search around nearby young stars.
guardian.co.uk – http://arxiv.org/pdf/1110.3808v1.pdf

Written by physicsgg

October 20, 2011 at 7:59 am

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How common are earth-moon planetary systems?

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This illustration shows a potential satellite-forming impact on a proto-planet. Credit: Michael Elser, University of Zurich

Sebastian Elser, Prof. Ben Moore and Dr. Joachim Stadel of the University of Zurich, Switzerland, in cooperation with Ryuji Morishima of NASA’s Jet Propulsion Laboratory, tried to estimate how common Earth-Moon planetary systems are. They have found that 1 in 12 Earth-like planets probably hosts a Moon-like satellite. Since the Moon might have played an important role in the history of life on Earth, this estimate is important concerning the search for habitable planets….. Read the rest of this entry »

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September 19, 2011 at 11:00 am

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What’s the weather like on other planets?

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Anyone wanting to holiday on Mars should be prepared to take shelter from passing sandstorms Photo: AFP/GETTY IMAGES

Mercury

he baby of the Solar system and closest to the Sun, smallest-planet Mercury has no atmosphere, so its weather forecast is usually fairly dull. However, visitors would be advised to either wrap up very warm, or slap on lots of SPF 50, depending on which part of the planet they stop off at – temperatures vary from -183C to 427C between the scorching subsolar point and freezing poles.

Venus

The hottest of all the planets, and second from the Sun, there’s no escaping the cloud cover on Venus. With an atmosphere that’s choked with carbon dioxide and nitrogen and suffused with sulphuric acid, glimpses of sunshine are unlikely. Mugginess doesn’t come close to describing the experience of sweating it out on the rocks with 92x the atmospheric pressure of Earth bearing down on you, trying to cool off in 480C heat.

Mars

The fourth planet from the Sun, Mars may have seen some heavy precipitation in the past but visitors these days would have to content themselves with strapping on their ice skates to explore the chilly polar regions. Expect to see blue sunsets and sunrises. Passing sandstorms on the horizon; take shelter.

Jupiter

Gigantic Jupiter is a gas planet, made up of hydrogen and helium. At 318 times the size of Earth, Jupiter gives off more heat than it gets from the Sun. Storms are highly likely as high pressure forces helium to become liquid, causing heavy rain, and winds of up to 360kph may be expected. Watch out for ammonia clouds, likely to be a common feature.

Saturn

The sixth planet from the Sun, Saturn is also made up of gas. The second-largest planet in the Solar system is not a hospitable place, with winds of up to 1,800kph, temperatures up to 14,727C at the core and a layer of ice 10 kilometres thick. Cloudy days expected, made up of ammonia, hydrogen and helium. Every 30 years or so, a super-storm called the Great White Spot brews up. Saturn is best avoided at this time.

Uranus

Stormy weather is forecast for this gas-and-ice planet, which is the third-largest and seventh from the Sun. Blue clouds of methane gas are expected, and visitors are advised to wear thermals to ward off the -197C chill.

Neptune

Brrr. The blue planet – furthest from the Sun – is also aptly the coldest, with temperatures plummeting to -224C. Another gas giant but with an icy core, expect similar weather to Uranus but at the more extreme end. Winds can reach 2,100kph.

http://www.telegraph.co.uk

Written by physicsgg

September 7, 2011 at 8:45 am

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Why Pluto is No Longer a Planet

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Is Pluto a planet? Does it qualify? For an object to be a planet, it needs to meet these three requirements defined by the IAU:

  • It needs to be in orbit around the Sun – Yes, so maybe Pluto is a planet.
  • It needs to have enough gravity to pull itself into a spherical shape – Pluto…check
  • It needs to have “cleared the neighborhood” of its orbit – Uh oh. Here’s the rule breaker. According to this, Pluto is not a planet.

What does “cleared its neighborhood” mean? As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects, they either consume them, or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit. The Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.

Let’s find out why Pluto is no longer considered a planet.
Pluto was first discovered in 1930 by Clyde W. Tombaugh at the Lowell Observatory in Flagstaff Arizona. Astronomers had long predicted that there would be a ninth planet in the Solar System, which they called Planet X. Only 22 at the time, Tombaugh was given the laborious task of comparing photographic plates. These were two images of a region of the sky, taken two weeks apart. Any moving object, like an asteroid, comet or planet, would appear to jump from one photograph to the next.
After a year of observations, Tombaugh finally discovered an object in the right orbit, and declared that he had discovered Planet X. Because they had discovered it, the Lowell team were allowed to name it. They settled on Pluto, a name suggested by an 11-year old school girl in Oxford, England (no, it wasn’t named after the Disney character, but the Roman god of the underworld).
The Solar System now had 9 planets.
Astronomers weren’t sure about Pluto’s mass until the discovery of its largest Moon, Charon, in 1978. And by knowing its mass (0.0021 Earths), they could more accurately gauge its size. The most accurate measurement currently gives the size of Pluto at 2,400 km (1,500 miles) across. Although this is small, Mercury is only 4,880 km (3,032 miles) across. Pluto is tiny, but it was considered larger than anything else past the orbit of Neptune.

Read also: NASA’s Hubble Discovers Another Moon Around Pluto

Over the last few decades, powerful new ground and space-based observatories have completely changed previous understanding of the outer Solar System. Instead of being the only planet in its region, like the rest of the Solar System, Pluto and its moons are now known to be just a large example of a collection of objects called the Kuiper Belt. This region extends from the orbit of Neptune out to 55 astronomical units (55 times the distance of the Earth to the Sun).
Astronomers estimate that there are at least 70,000 icy objects, with the same composition as Pluto, that measure 100 km across or more in the Kuiper Belt. And according to the new rules, Pluto is not a planet. It’s just another Kuiper Belt object.

Here’s the problem. Astronomers had been turning up larger and larger objects in the Kuiper Belt. 2005 FY9, discovered by Caltech astronomer Mike Brown and his team is only a little smaller than Pluto. And there are several other Kuiper Belt objects in that same classification.

Astronomers realized that it was only a matter of time before an object larger than Pluto was discovered in the Kuiper Belt.
And in 2005, Mike Brown and his team dropped the bombshell. They had discovered an object, further out than the orbit of Pluto that was probably the same size, or even larger. Officially named 2003 UB313, the object was later designated as Eris. Since its discovery, astronomers have determined that Eris’ size is approximately 2,600 km (1,600 miles) across. It also has approximately 25% more mass than Pluto.

With Eris being larger, made of the same ice/rock mixture, and more massive than Pluto, the concept that we have nine planets in the Solar System began to fall apart. What is Eris, planet or Kuiper Belt Object; what is Pluto, for that matter? Astronomers decided they would make a final decision about the definition of a planet at the XXVIth General Assembly of the International Astronomical Union, which was held from August 14 to August 25, 2006 in Prague, Czech Republic.

Astronomers from the association were given the opportunity to vote on the definition of planets. One version of the definition would have actually boosted the number of planets to 12; Pluto was still a planet, and so were Eris and even Ceres, which had been thought of as the largest asteroid. A different proposal kept the total at 9, defining the planets as just the familiar ones we know without any scientific rationale, and a third would drop the number of planets down to 8, and Pluto would be out of the planet club. But, then… what is Pluto?

In the end, astronomers voted for the controversial decision of demoting Pluto (and Eris) down to the newly created classification of “dwarf planet”.

Is Pluto a planet? Does it qualify? For an object to be a planet, it needs to meet these three requirements defined by the IAU:

  • It needs to be in orbit around the Sun – Yes, so maybe Pluto is a planet.
  • It needs to have enough gravity to pull itself into a spherical shape – Pluto…check
  • It needs to have “cleared the neighborhood” of its orbit – Uh oh. Here’s the rule breaker. According to this, Pluto is not a planet.

What does “cleared its neighborhood” mean? As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects, they either consume them, or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit. The Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.

Any object that doesn’t meet this 3rd criteria is considered a dwarf planet. And so, Pluto is a dwarf planet. There are still many objects with similar size and mass to Pluto jostling around in its orbit. And until Pluto crashes into many of them and gains mass, it will remain a dwarf planet. Eris suffers from the same problem.

It’s not impossible to imagine a future, though, where astronomers discover a large enough object in the distant Solar System that could qualify for planethood status. Then our Solar System would have 9 planets again.

Even though Pluto is a dwarf planet, and no longer officially a planet, it’ll still be a fascinating target for study. And that’s why NASA has sent their New Horizons spacecraft off to visit it. New Horizons will reach Pluto in July 2015, and capture the first close-up images of the (dwarf) planet’s surface.

Space enthusiasts will marvel at the beauty and remoteness of Pluto, and the painful deplaneting memories will fade. We’ll just be able to appreciate it as Pluto, and not worry how to categorize it. At least now you know why Pluto was demoted.

http://www.universetoday.com/13573/why-pluto-is-no-longer-a-planet/

Density vs mass of all planets (+ Pluto , Moon and Sun)

Written by physicsgg

July 20, 2011 at 4:25 pm

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