Posted on by Anne Minard

Fermilab Putting the Squeeze on Higgs Boson

The Standard Model describes the interactions of fundamental particles. The W boson, the carrier of the electroweak force, has a mass that is fundamentally relevant for many predictions, from the energy emitted by our sun to the mass of the elusive Higgs boson. Credit: Fermilab

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Scientists at the Department of Energy’s Fermi National Accelerator Laboratory have achieved the world’s most precise measurement of the mass of the W boson by a single experiment. Combined with other measurements, a tighter understanding of the W boson mass will also lead researchers closer to the mass of the elusive Higgs boson particle.

The Higgs particle is a theoretical but as yet unseen particle, also called the “God particle,” that is believed to give other particles their mass. The W boson, which is about 85 times heavier than a proton, enables radioactive beta decay and makes the sun shine. 

Today’s announcement marks the second major discovery in a week for the international DZero collaboration at Fermilab. Earlier this week, the group announced the production of a single top quark at Fermilab’s Tevatron collider. 

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For the W mass precision measurement, the DZero collaboration analyzed about 500,000 decays of W bosons into electrons and neutrinos and determined the particle's mass with a precision of 0.05 percent. Credit: Fermilab

DZero is an international experiment of about 550 physicists from 90 institutions in 18 countries. It is supported by the U.S. Department of Energy, the National Science Foundation and a number of international funding agencies. In the last year, the collaboration has published 46 scientific papers based on measurements made with the DZero particle detector.

The W boson is a carrier of the weak nuclear force and a key element of the Standard Model of elementary particles and forces, which also predicts the Higgs boson. Its  exact mass is crucial for calculations  to estimate the likely mass of the Higgs boson by studying its subtle quantum effects on the W boson and the top quark, an elementary particle that was discovered at Fermilab in 1995.

Scientists working on the DZero experiment now have measured the mass of the W boson with a precision of 0.05 percent. The exact mass of the particle measured by DZero is 80.401 +/- 0.044 GeV/c^2. The collaboration presented its result at the annual conference on Electroweak Interactions and Unified Theories known as Rencontres de Moriond on Sunday.

“This beautiful measurement illustrates the power of the Tevatron as a precision instrument and means that the stress test we have ordered for the Standard Model becomes more stressful and more revealing,” said Fermilab theorist Chris Quigg.

The DZero team determined the W mass by measuring the decay of W bosons to electrons and electron neutrinos. Performing the measurement required calibrating the DZero particle detector with an accuracy around three hundredths of one percent, an arduous task that required several years of effort from a team of scientists including students.

Since its discovery at the European laboratory CERN in 1983, many experiments at Fermilab and CERN have measured the mass of the W boson with steadily increasing precision. Now DZero achieved the best precision by the painstaking analysis of a large data sample delivered by the Tevatron particle collider at Fermilab. The consistency of the DZero result with previous results speaks to the validity of the different calibration and analysis techniques used.

“This is one of the most challenging precision measurements at the Tevatron,” said DZero co-spokesperson Dmitri Denisov, of Fermilab. “It took many years of efforts from our collaboration to build the 5,500-ton detector, collect and reconstruct the data and then perform the complex analysis to improve our knowledge of this fundamental parameter of the Standard Model.“

Source: Fermilab

Posted on by Nancy Atkinson

Top Ten Gamma Ray Sources from the Fermi Telescope

This view from NASA's Fermi Gamma-ray Space Telescope is the deepest and best-resolved portrait of the gamma-ray sky to date. The image shows how the sky appears at energies more than 150 million times greater than that of visible light. Among the signatures of bright pulsars and active galaxies is something familiar -- a faint path traced by the sun. Credit: NASA/DOE/Fermi LAT Collaboration

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The Fermi Telescope is seeing a Universe ablaze with Gamma Rays! A new map combining nearly three months of data from the Fermi Gamma-ray Space Telescope is giving astronomers an unprecedented look at the high-energy cosmos.

“Fermi has given us a deeper and better-resolved view of the gamma-ray sky than any previous space mission,” said Peter Michelson, the lead scientist for the spacecraft’s Large Area Telescope (LAT) at Stanford University. “We’re watching flares from supermassive black holes in distant galaxies and seeing pulsars, high-mass binary systems, and even a globular cluster in our own.”

The sources of these gamma rays come from within our solar system to galaxies billions of light-years away. To show the variety of the objects the LAT is seeing, the Fermi team created a “top ten” list comprising five sources within the Milky Way and five beyond our galaxy.

The top five sources within our galaxy are:

The Sun. Now near the minimum of its activity cycle, the sun would not be a particularly notable source except for one thing: It’s the only one that moves across the sky. The sun’s annual motion against the background sky is a reflection of Earth’s orbit around the sun.

“The gamma rays Fermi now sees from the sun actually come from high-speed particles colliding with the sun’s gas and light,” Thompson notes. “The sun is only a gamma-ray source when there’s a solar flare.” During the next few years, as solar activity increases, scientists expect the sun to produce growing numbers of high-energy flares, and no other instrument will be able to observe them in the LAT’s energy range.

LSI +61 303. This is a high-mass X-ray binary located 6,500 light-years away in Cassiopeia. This unusual system contains a hot B-type star and a neutron star and produces radio outbursts that recur every 26.5 days. Astronomers cannot yet account for the energy that powers these emissions.

PSR J1836+5925. This is a pulsar — a type of spinning neutron star that emits beams of radiation — located in the constellation Draco. It’s one of the new breed of pulsars discovered by Fermi that pulse only in gamma rays.

47 Tucanae. Also known as NGC 104, this is a sphere of ancient stars called a globular cluster. It lies 15,000 light-years away in the southern constellation Tucana.

The Large Area Telescope (LAT) on Fermi detects gamma-rays through matter (electrons) and antimatter (positrons) they produce after striking layers of tungsten. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab
The Large Area Telescope (LAT) on Fermi detects gamma-rays through matter (electrons) and antimatter (positrons) they produce after striking layers of tungsten. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab

Click here to view an animation of the LAT

Unidentified. More than 30 of the brightest gamma-ray sources Fermi sees have no obvious counterparts at other wavelengths. This one, designated 0FGL J1813.5-1248, was not seen by previous missions, and Fermi’s LAT sees it as variable. The source lies near the plane of the Milky Way in the constellation Serpens Cauda. As a result, it’s likely within our galaxy — but right now, astronomers don’t know much more than that.

The top five sources beyond our galaxy are:

NGC 1275. Also known as Perseus A, this galaxy at the heart of the Perseus Galaxy Cluster is known for its intense radio emissions. It lies 233 million light-years away.

Hubble Space Telescope image of a blazar galaxy. Credit: NASA
Hubble Space Telescope image of a blazar galaxy. Credit: NASA

3C 454.3. This is a type of active galaxy called a “blazar.” Like many active galaxies, a blazar emits oppositely directed jets of particles traveling near the speed of light as matter falls into a central supermassive black hole. For blazars, the galaxy happens to be oriented so that one jet is aimed right at us. Over the time period represented in this image, 3C 454.3 was the brightest blazar in the gamma-ray sky. It flares and fades, but for Fermi it’s never out of sight. The galaxy lies 7.2 billion light-years away in the constellation Pegasus.

PKS 1502+106. This blazar is located 10.1 billion light-years away in the constellation Boötes. It appeared suddenly, briefly outshone 3C 454.3, and then faded away.

PKS 0727-115. This object’s location in the plane of the Milky Way would lead one to expect that it’s a member of our galaxy, but it isn’t. Astronomers believe this source is a type of active galaxy called a quasar. It’s located 9.6 billion light-years away in the constellation Puppis.

Unidentified. This source, located in the southern constellation Columba, is designated 0FGL J0614.3-3330 and probably lies outside the Milky Way. “It was seen by the EGRET instrument on NASA’s earlier Compton Gamma Ray Observatory, which operated throughout the 1990s, but the nature of this source remains a mystery,” Thompson says.

The LAT scans the entire sky every three hours when operating in survey mode, which is occupying most of the telescope’s observing time during Fermi’s first year of operations. These snapshots let scientists monitor rapidly changing sources.

The all-sky image released today shows us how the cosmos would look if our eyes could detect radiation 150 million times more energetic than visible light. The view merges LAT observations spanning 87 days, from August 4 to October 30, 2008.

Source: NASA

Posted on by Nancy Atkinson

Watch Discovery Light Up the Night Sky

Shuttle Discovery on the launchpad. Credit: NASA/Bill Ingalls

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2nd UPDATE: (6:45 EDT) Mission managers have reset the launch of Discovery on STS-119 to no earlier than Sunday, March 15 at 7:43:38 p.m. EDT. Engineers will troubleshoot problems with a leaky hydrogen line.

UPDATE: (2:25 pm EDT) Launch scrub due to leak in hydrogen line while fueling. Rats! Latest news is that NASA will try again tomorrow to launch. The launch time has now been set for 8:54 pm EDT on Thursday, March 12.

Space shuttle Discovery will light up the night sky with a Wednesday Thursday Sunday evening launch, at 9:20 pm EDT (1:20 am GMT). 8:54 pd EDT (12:54 am GMT). 7:43 pm EDT (11:443 pm GMT). Mission managers have given the go-ahead for filling the external fuel tank with the super-cold propellants and the weather looks favorable, so things are looking good for an on-time launch. Night launches are always gorgeous to watch, and there are a plethora of ways to follow the launch. First and foremost, if you live along the Eastern coast of the United States, you may be able to see the shuttle rise from Earth with your own eyes! If the skies are clear in your area, look low in the sky at launch time, about 5 to 15 degrees above the horizon, depending on your viewing point. You’ll see a light moving quite fast, streaking across 90 degrees of azimuth in less than a minute.

Below is a list of the different webcasts and feeds that will be showing the launch live for those of us that don’t live on the US Eastern seaboard. Plus, I’ll be Twittering during pre-launch and launch if you want to join me.

Of course, the launch will be shown live on NASA TV. If NASA TV isn’t available in your area via cable or satellite, watch it on the web.

Spaceflightnow.com will be having a live webcast featuring Miles O’Brien, former astronaut LeRoy Chiao and David Waters starting at at 4:30 p.m. EDT (2030 GMT) Wednesday.

SpaceVidCast will also be showing a live feed, with interesting banter from their hosts, Cariann and Ben Higginbotham.

Commander Lee Archambault will lead Discovery’s crew of seven, along with Pilot Tony Antonelli, and Mission Specialists Joseph Acaba, John Phillips, Steve Swanson, Richard Arnold and Japan Aerospace Exploration Agency astronaut Koichi Wakata on mission STS-119 to the International Space Station.

The Discovery crew members will bring the S6 truss segment and install the final set of power-generating solar arrays to the International Space Station. The S6 truss will complete the backbone of the station and provide one-fourth of the total power needed to support a crew of six. It also will increase the surface area of the ISS to over an acre. The sunlight reflected from this surface area will make the ISS the 2nd brightest object in the night sky, after the moon. Here’s info on where and how to look for the ISS in the night sky.

Posted on by Ian O'Neill

Phoenix Team Divided: Are the Mars Liquid Water Observations a “Matter of Belief”?

Detail of the three controvercial images of the Phoenix Mars Lander's leg. Are they droplets of water? (Renno, et al., NASA)

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Last month, it was announced that in the few days after the landing of the Phoenix lander in May 2008, the camera attached to the robotic arm captured visual evidence of (what appeared to be) droplets of water, almost like condensation forming on the leg of the lander. In three images dated on sol 8, sol 31 and sol 44 of the mission, the droplets appear to move, in a fluid-like manner. Although a recent publication indicates this oddity could be a water-perchlorate mix (where the toxic salt acts as a potent anti-freeze, preventing the water from freezing and subliming), other members of the Phoenix team are very dubious, saying that there is another, more likely explanation…

One of the key components necessary for the survival of life on Earth is water, especially when the water is in a liquid state. This is an easy proposition on our planet, as the atmospheric pressures and temperatures are just right for the majority of water on Earth to be in a usable liquid state. Should liquid water be discovered on another planet however, where the conditions are often too hot or too cold (or when atmospheric pressure is too low) for water to be found in a liquid state, you’d expect there to be some excitement. When that other planet is Mars, the focal point of the search for basic extraterrestrial life, this excitement will be tempered with intense scrutiny.

In February’s article, Nilton Renno from the University of Michigan and Phoenix mission team scientist, announced results from his team’s research into some odd-looking blobs on one of the lander’s legs. Renno’s hypothesis, to be presented on March 23rd at the Lunar and Planetary Science Conference in Houston (TX), focuses on the possibility that the newly discovered toxic compound, perchlorate, may hold the key to the possibility of liquid water on the Martian surface. We know on Earth, briny (salty) water has a lower freezing point than pure water, and Renno suspects that this might be the case for water on the surface of Mars. However, rather than regular salt, the toxic perchlorate salt is mixed with water in the regolith, allowing it to sustain its liquid state.

Although a very interesting proposition, Renno’s results are based on only photographic evidence of what appears to be blobs of water. Other Phoenix scientists are emphasising that the theory is controversial, citing far simpler answers for the observations.

“There’s a matter of belief at some level,” said Peter Smith from the University of Arizona in Tucson and principal Phoenix investigator. “I can’t say I agree with every statement in the [Renno] paper.”

Michael Hecht, the lead scientist for the instrument that discovered perchlorate in the first place, goes as far to say a perchlorate brine on the Martian surface is very unlikely. Simpler explanations for the apparent dynamic movement of the “liquid” blobs could be attributed to changing shadows. Although perchlorate acts as an efficient “sponge”, condensing water vapour from the surrounding air, the temperatures stated in the paper are actually too warm to form liquid droplets of perchlorate brine.

“I just don’t think it’s the likely explanation,” Hecht said. “It’s just plain old frost, nothing more.”

Looking at the Phoenix images (top), I am a little suspicious about the lifetime of these proposed “liquid” droplets. From sol 8 to sol 44, there is little dramatic change in the locations or sizes of these features. 36 sols of long-term droplets of liquid water seems like a very long time considering the very low atmospheric pressures we are dealing with. Surely liquid brine droplets will dissipate (through evaporation, rather than sublimation) far quicker than 36 sols? Granted, there may be further condensation from the atmosphere (topping up the presence of the liquid), but wouldn’t there be more motion in the blobs if this were the case? This said, I am not familiar with perchlorate brine, so this might well be a characteristic of this cold liquid.

It looks like Renno’s research will make for a very interesting presentation on March 23rd at the Lunar and Planetary Science Conference, sure to provoke a lively debate…

Source: Space.com

Posted on by Nancy Atkinson

Hubble, VLT Team Up to View the History of the Universe in 3-D

NASA/ESA Hubble Space Telescope images of the three galaxies studied by a team of astronomers who try to understand how galaxies formed when the Universe was half its current age (upper panels). The same galaxies were then studied with the FLAMES/GIRAFFE instrument on ESO’s Very Large Telescope (VLT) to probe the motions of gas in these objects (lower panels). P

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Once upon a time, before our Sun and Earth existed, distant galaxies were being created. Because this happened so long ago, astronomers know very little about how these galaxies formed. But now, by combining the Hubble Space Telescope’s acute vision with the Very Large Telescope’s spectrograph, astronomers have obtained exceptional 3-D views of distant galaxies, seen when the Universe was half its current age. By looking at this unique “history book” of our Universe, scientists hope to solve the puzzle of how galaxies formed in the remote past.

Hubble allows fine details of galaxies to be seen, while the VLT’s FLAMES/GIRAFFE spectrograph can obtain simultaneous spectra from small areas of extended objects, and resolving the motions of the gas in these distant galaxies.

“This unique combination of Hubble and the VLT allows us to model distant galaxies almost as nicely as we can close ones,” said François Hammer, who led the team. “In effect, FLAMES/GIRAFFE now allows us to measure the velocity of the gas at various locations in these objects. This means that we can see how the gas is moving, which provides us with a three-dimensional view of galaxies halfway across the Universe.”

The team has been reconstructing the history of about one hundred remote galaxies that have been observed with both Hubble and GIRAFFE on the VLT. The first results are coming in and have already provided useful insights for three galaxies.

Combining the twin strengths of the NASA/ESA Hubble Space Telescope’s acute eye, and the capacity of ESO’s Very Large Telescope (VLT) to probe the motions of gas in tiny objects. Credit: ESO
Combining the twin strengths of the NASA/ESA Hubble Space Telescope’s acute eye, and the capacity of ESO’s Very Large Telescope (VLT) to probe the motions of gas in tiny objects. Credit: ESO

In one galaxy, GIRAFFE revealed a region full of ionized gas, that is, hot gas composed of atoms that have been stripped of one or several electrons. This is normally due to the presence of very hot, young stars. However, even after staring at the region for more than 11 days, Hubble did not detect any stars! “Clearly this unusual galaxy has some hidden secrets,” said Mathieu Puech, lead author of one of the papers reporting this study. Comparisons with computer simulations suggest that the explanation lies in the collision of two very gas-rich spiral galaxies. The heat produced by the collision would ionise the gas, making it too hot for stars to form.

Another galaxy that the astronomers studied showed the opposite effect. There they discovered a bluish central region enshrouded in a reddish disc, almost completely hidden by dust. “The models indicate that gas and stars could be spiralling inwards rapidly,” said Hammer. This might be the first example of a disc rebuilt after a major merger.

Finally, in a third galaxy, the astronomers identified a very unusual, extremely blue, elongated structure — a bar — composed of young, massive stars, rarely observed in nearby galaxies. Comparisons with computer simulations showed the astronomers that the properties of this object are well reproduced by a collision between two galaxies of unequal mass.

Watch a movie simulating the motion of the collision between these two galaxies.

“The unique combination of Hubble and FLAMES/GIRAFFE at the VLT makes it possible to model distant galaxies in great detail, and reach a consensus on the crucial role of galaxy collisions for the formation of stars in a remote past,” says Puech. “It is because we can now see how the gas is moving that we can trace back the mass and the orbits of the ancestral galaxies relatively accurately. Hubble and the VLT are real ‘time machines’ for probing the Universe’s history,” added Sébastien Peirani, lead author of another paper reporting on this study.

The astronomers are now extending their analysis to the whole sample of galaxies observed. “The next step will then be to compare this with closer galaxies, and so, piece together a picture of the evolution of galaxies over the past six to eight billion years, that is, over half the age of the Universe,” said Hammer.

Source: ESO

Posted on by Fraser Cain

Earth’s Interior

The Earths interior (University of Chicago)

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Take a look down beneath your feet. You’re standing on the Earth’s crust. Although it seems limitless, the Earth’s crust only accounts for less than 1% of the Earth’s interior. Let’s take a look at everything that’s inside the Earth.

The Earth’s crust is the outer shell of the Earth. This is the part that has cooled down enough to solidify into rock. The crust extends down 30 km to 80 km underneath the continents, and only 5 km beneath the oceans. As you travel down through the crust, temperatures increase. The crust is broken up into several tectonic plates which “float” on top of the Earth’s mantle. In some regions, plates are sliding underneath one another, recycling rocks into the Earth. The crust beneath the middle of the oceans is spreading apart, and new material is welling up.

Beneath the crust is the largest part of the Earth’s interior: the mantle, which makes up about 84% of the Earth’s volume. This region extends down to a depth of 2,890 km. As you travel down through the mantle, temperatures increase immensely; they start at 500 C near the crust, and get to well over 4000 C at the boundary to the core. The mantle is mostly solid, but it acts like a viscous fluid, and experiences convection. Hot blobs of rock rise up from regions around the core through the mantle, give up their heat, and then sink back down.

At the very center of the Earth lies the core. This is a solid sphere of metal 2,440 km across surrounded by a layer of liquid metal. Scientists think that mostly made of iron (80%), with the rest composed of other heavy metals, like nickel, gold, platinum and even uranium. The core is slowly rotating compared to the crust, so that the core completes one rotation every 1000 years or so. The Earth’s magnetic field is though to be generated by the convection of hot metal in the Earth’s outer core. This field protects the Earth from the Sun’s solar wind; there probably wouldn’t be life on Earth without this field.

We have written many articles about the Earth for Universe Today. Here’s an article about the discovery of the Earth’s inner, inner core.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Sources:
http://www.portal.gsi.gov.in/portal/page?_pageid=127,687643&_dad=portal&_schema=PORTAL
http://en.wikipedia.org/wiki/Mantle_%28geology%29
http://www.windows2universe.org/earth/Interior_Structure/interior.html

Posted on by Nancy Atkinson

Debris From Satellite Collision to Start Entering Earth’s Atmosphere

Map of debris from satellite collision. Credit: Dan Deak and Spaceweather.com

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Debris from the satellite collision that occurred on February 10th will soon start entering Earth’s atmosphere. 355 debris fragments from the collision between the Cosmos 2251 and the Iridium 33 satellites are being tracked by US Strategic Command, and one fragment will enter the atmosphere on March 12, followed by one on March 28th and another on March 30th. According to Spaceweather.com, these are likely centimeter-sized pieces that will disintegrate in the atmosphere, posing no threat to people on the ground. Each fragment is cataloged and tracked.

The Cosmos 2251 was bigger and possessed about one and a half times more mass than Iridium 33, and appears to have produced more than twice the number of fragments. “As of March 7th, there were 355 cataloged fragments of Cosmos 2251 and 159 fragments of Iridium 33,” says Daniel Deak who prepared the above orbit-map for Spaceweather.com. “The Cosmos fragments are not only more numerous, but also more widely scattered, ranging in altitude from 198 km to 1689 km. For comparison, Iridium fragments are confined to altitudes between 582 km and 1262 km.”

The extra scatter of Cosmos debris is not fully understood. Impact geometry could explain the spread, but no one knows exactly how the two complex vehicles struck one another. However, Cosmos 2251 was pressurized and might have ruptured and blown apart.

The upcoming shuttle mission is not in immediate danger from debris, although the risk of impact increased by 6%. The International Space Station also is not in danger. “NASA has recognized from the first day [of the collision] that the risks to both ISS and STS-119 have increased,” says Nick Johnson, Chief Scientist for Orbital Debris at the Johnson Space Center. “However, those increases have been relatively minor in comparison to the background environment.”

Source: Spaceweather.com

Posted on by Fraser Cain

Why is the Earth Round?

Earth as seen from the ISS. Credit: NASA

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Don’t listen to the Flat Earth Society, they’re wrong; the Earth is round. But did you ever wonder why the Earth is round? It all comes down to gravity.

One of the effects of mass is that it attracts other mass. For small objects, like your computer, your car, and even a building, the force of gravity is tiny. But when you have millions, and even trillions of tonnes of mass, the effect of the gravity really builds up. All of the mass pulls on all the other mass, and it tries to create the most efficient shape… a sphere.

For smaller objects, like asteroids, the force of gravity trying to pull the object into a sphere isn’t enough to overcome the strength of the rock keeping it in shape. But once you get above a certain mass and size, the strength of the object can’t stop the force of gravity from pulling it into a sphere. Objects larger than about 1,000 km in size are able to pull themselves into a sphere.

In fact, the International Astronomical Union decided in 2006 that this ability was one of the requirements for an object to be considered a planet. They must orbit the Sun, they need to have cleared out all the smaller objects in their orbit, and they need to have enough gravity to pull themselves into a sphere.

When an object has the gravity to pull itself into a sphere, astronomers say that it’s in hydrostatic equilibrium. And that’s why the Earth is round.

Of course, the Earth isn’t perfectly round. Because it’s turning on its axis approximately once every 24 hours, the Earth’s equator bulges outwards. And there are mountains and valleys that make the Earth’s surface rough.

We have written many articles about the Earth for Universe Today. Here’s an article about how round the Earth really is.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, answering a few questions, like why is Earth round. This was part of our tour through the Solar System – Episode 51: Earth.

Posted on by Jerry Coffey

Density of the Earth

The Earths interior (University of Chicago)

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The density of the Earth is 5.513 g/cm3. This is an average of all of the material on the planet. Water is much less dense than iron, hence an average is needed for ease of use. Earth is the most dense planet in the Solar System; however, if gravitational compression where factored out, the second most dense planet, Mercury, would be more dense. The density of Earth is calculated by dividing the planet’s mass by its volume, then simplifying from kg/km to g/cm cubed.

Here is the density of the other planets in our Solar System so you can compare to Earth’s.

Mercury 5.43 g/cm3
Venus 5.243 g/cm3
Mars 3.934 g/cm3
Jupiter 1.326 g/cm3
Saturn 0.687 g/cm3
Uranus 1.270 g/cm3
Neptune 1.638 g/cm3
The Sun 1.408 g/cm3

Just knowing the density of a planet is not much information. It sort of only gives a partial picture. Here are a few more interesting facts about the Earth that may help you understand our planet a little more.

The Moon is thought to have been formed when a large asteroid or a planetesimal impacted Earth. The Moon is the portion that was thrown back into space and the particles that accreted to it. Scientist think that other planets may have obtained some of their moons in a similar manner. The Earth is the only planet with a single Moon, but has two quasi-satellites 3753 Cruithne and 2002 AA29.

The Sun is constantly evolving. In a few billion years it will begin to heat up on its way to the red giant phase of a star’s life. Along the way it will become hot enough to destroy life on Earth. The question will become how will humans survive. Colonizing other celestial objects is one option. Some scientists have developed a theoretical way to move the entire planet. It would require finding an asteroid large enough to perturb Earth’s orbit and push away from the Sun. Colonizing another planet could actually be easier.

Despite a lot of internet hype, there is no credible threat to the Earth that will coincide with the end of the Mayan calendar. The Mayan calender does not even end, 2012 marks the end of the current long-count period. 2013 marks the beginning of another.

The density of Earth is one of thousands of interesting facts that you find about your home planet. Here at Universe Today, we hope that you want to find many more and continue to research the world around you.

We have written many articles about density for Universe Today. Here’s an article about the density of the Sun, and here’s one about the density of Mars.

Want more resources on the Earth? Here’s a link to NASA’s Human Spaceflight page, and here’s NASA’s Visible Earth.

We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.

Sources:
NASA
Physics Forums

Posted on by Nancy Atkinson

Live From Space: Streaming Webcam Now Available

Earth as seen from the ISS. Credit: NASA

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It’s not exactly what Al Gore had in mind, but its close. Live streaming video is now available every day of the week from the International Space Station. The video will show views of Earth and the exterior structure of the station, as seen from cameras mounted outside the ISS, and other times, activities going on inside the station. If you regularly watch NASA TV online, just go to the same website, and now there’s another choice of channels. Just click on the “Live Space Station Video” tab to enjoy. The Earth views will usually be seen during what is the crew off-duty or sleep periods, usually from about 6 pm to 6 am GMT (1 p.m. to 1 a.m. CST.) During times when the crew is awake and working, selected video will be available, accompanied by audio of communications between Mission Control and the astronauts. Be advised that during working hours when there are special events going on — for example, today as I’m writing this there is a spacewalk taking place — the public channel offers better views and commentary.

During times when the shuttle is docked to the station, the stream will include video and audio of those activities. Whenever video isn’t available, a graphical world map will be shown that depicts the station’s location in orbit above the Earth using real-time telemetry sent to Mission Control from the station.
Since the station orbits the Earth once every 90 minutes, it sees a sunrise or a sunset every 45 minutes. When the station is in darkness, external camera video may appear black, but also may provide great views of city lights below.

The streaming video is being webcast as part of NASA’s celebration of the 10th anniversary of the space station in orbit.

To find out when you can go outside and look back at the station overhead, check out NASA’s page for sighting opportunities.

Source: NASA