Posted on by Fraser Cain

What Type of Planet is Mercury?

Planet Mercury
Planet Mercury

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Mercury is the smallest and innermost planet in the Solar System. But what type of planet is Mercury?

Mercury is classified as a terrestrial planet. The terrestrial planets include the 4 rocky worlds in the inner Solar System: Mercury, Venus, Earth and Mars. The term “terrestrial” comes from the latin term “terra”, meaning Earth. So the terrestrial planets are similar to Earth.

For example, the average density of Mercury is 5.427 g/cm3. Compare this to Earth’s density of 5.515 g/cm3. Planets with this kind of density are made up of mostly rock and metal. Compare this to the density of Saturn, at 0.687 g/cm3. Saturn is so light that it would float on water is you had a pool large enough.

Mercury is made up of distinct layers, similar to Earth. It has a large metallic core, made of solid or liquid iron. This is surrounded by a mantle of hot rock, and this is surrounded by a thin crust of rock. There are no active volcanoes on Mercury, but astronomers think the planet might still be releasing volcanic gasses through vents.

The terrestrial planets are also unusual because they have few or no moons. Mercury has no moons, and neither does Venus. Mars has two tiny asteroid-like moons, and only Earth has a moon of any significant size.

We have written many articles about the planets in the Solar System. Here’s an article about the terrestrial planets, and here’s an article about the gas giants.

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’ve also recorded an entire episode of Astronomy Cast all about Mercury. Listen here, Episode 49: Mercury.

Posted on by Nancy Atkinson

Hubble Delves into Two Recent Jupiter Mysteries

Detailed observations made by the NASA/ESA Hubble Space Telescope have led researchers to believe that the flash of light seen on Jupiter on 3 June was a meteor. Credit: NASA, ESA, M. H. Wong (University of California, Berkeley, USA), H. B. Hammel (Space Science Institute, Boulder, Colorado, USA), A. A. Simon-Miller (Goddard Space Flight Center, Greenbelt, Maryland, USA) and the Jupiter Impact Science Team.

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Jupiter has a few mysteries these days. Between an equatorial belt that has gone missing and an impact that didn’t leave a mark, astronomers decided they needed to put the Hubble Space Telescope on the case. New and detailed observations from the venerable space telescope have provided some insights into these two recent puzzling events.

At 22:31 (CEST) on June 3, 2010 Australian amateur astronomer Anthony Wesley saw a two-second-long flash of light on the disc of Jupiter, captured from a live video feed from his telescope. In the Philippines, amateur astronomer Chris Go confirmed that he had simultaneously recorded the transitory event on video. Wesley was also the discoverer of the now world-famous July 2009 impact.

Astronomers around the world suspected that something significant must have hit the giant planet to unleash a flash of energy bright enough to be seen here on Earth, about 770 million kilometers away. But they didn’t know how just how big it was or how deeply it had penetrated into the atmosphere. Over the past two weeks there have been ongoing searches for the “black-eye” pattern of a deep direct hit like those left by former impactors.

Astronomers turned Hubble’s Wide Field Camera 3 aboard the NASA/ESA Hubble Space Telescope on June 7, and found no sign of debris above Jupiter’s cloud tops. This means that the object didn’t descend beneath the clouds and explode as a fireball. If it had, then dark sooty blast debris would have been ejected and would have rained down onto the clouds.

Instead the flash is thought to have come from a giant meteor burning up high above Jupiter’s cloud tops, which did not plunge deep enough into the atmosphere to explode and leave behind any telltale cloud of debris, as seen in previous Jupiter collisions.

“The cloud tops and the impact site would have appeared dark in the ultraviolet and visible images due to debris from an explosion,” said team member Heidi Hammel of the Space Science Institute in Boulder, Colorado. “We can see no feature that has those distinguishing characteristics in the known vicinity of the impact, suggesting there was no major explosion and no ‘fireball’.”

Dark smudges marred Jupiter’s atmosphere when a series of fragments of Comet Shoemaker-Levy 9 hit Jupiter in July 1994, and a similar dark area formed in July 2009 when a suspected asteroid slammed into Jupiter. The latest intruder is estimated to be only a fraction of the size of these previous impactors and is thought to have been a meteor.

So, Wesley and Go were fortunate to have spotted the flash.

“Observations of these impacts provide a window on the past — onto the processes that shaped our Solar System in its early history,” said team member Leigh Fletcher of the University of Oxford, UK. “Comparing the two collisions — from 2009 and 2010 — will hopefully yield insights into the types of impact processes in the outer Solar System, and the physical and chemical response of Jupiter’s atmosphere to these amazing events.”

These Hubble images of Jupiter taken 11 months apart show the Southern Equatorial Belt has disappeared. Credit: NASA, ESA, M. H. Wong (University of California, Berkeley, USA), H. B. Hammel (Space Science Institute, Boulder, Colorado, USA), A. A. Simon-Miller (Goddard Space Flight Center, Greenbelt, Maryland, USA) and the Jupiter Impact Science Team.

Since Hubble was now trained on Jupiter, astronomers used the opportunity to get a close-up look at changes in Jupiter’s atmosphere following the disappearance of the dark cloud feature known as the Southern Equatorial Belt several months ago.

In the Hubble view, a slightly higher altitude layer of white ammonia ice crystal clouds appears to obscure the deeper, darker belt clouds. “Weather forecast for Jupiter’s Southern Equatorial Belt: cloudy with a chance of ammonia,” Hammel said.

The team predicts that these ammonia clouds should clear out in a few months, as they have done in the past. The clearing of the ammonia cloud layer should begin with a number of dark spots like those seen by Hubble along the boundary of the south tropical zone.

“The Hubble images tell us these spots are holes resulting from localized downdrafts. We often see these types of holes when a change is about to occur,” said Amy Simon-Miller from Goddard Space Flight Center. .

“The Southern Equatorial Belt last faded in the early 1970s. We haven’t been able to study this phenomenon at this level of detail before,” Simon-Miller added. “The changes of the last few years are adding to an extraordinary database on dramatic cloud changes on Jupiter.”

Source: ESA’s Hubble website

Posted on by Nancy Atkinson

Separation Camera Takes Full Images and ‘Movie’ of IKAROS Solar Sail

Image of the fully deployed IKAROS solar sail, taken by a separation camera. Credit: JAXA

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Two small “separation cameras” were ejected from JAXA’s (Japan Aerospace Exploration Agency) IKAROS solar sail, which successfully took some amazing full images of the fully deployed sail. The cameras are quite small, cylindrical in shape about 6 cm in diameter and height. They were ejected from the sail using a spring, and then they looked back at IKAROS, and relayed the images wirelessly. The cameras are now floating off into space, having done their job of taking these images. Below, an animation, or movie made by combining several images.


An animation created from several pictures taken by the DCAM2 on IKAROS. The camera rotated as it was ejected from the solar sail, so it is rotating, not IKAROS. Credit: JAXA

From the JAXA press release:

We will measure and observe the power generation status of the thin film solar cells, accelerate the satellite by photon pressure, and verify the orbit control through that acceleration. Through these activities, we will ultimately aim at acquiring navigation technology through the solar sail.

So, now that we know the sail is fully deployed, next comes the big test of whether solar sailing will actually work. This is huge, to finally have the opportunity to test a solar sail in space.

Close-up of the middle of the IKAROS solar sail, taken by the DCAM2. Credit: JAXA

From the IKAROS blog, speaking as the cameras:

Unfortunately I only have the battery, and…working time is very short for about 15 minutes after I do my best work is a planets around the Sun, the world’s smallest man-made flying with IKAROS continue.

Translation: these tiny cameras only had about 15 minutes to do their job of taking pictures before becoming dead little satellites orbiting around the sun.

IKAROS was launched on May 21, 2010 from the Tanegashima Space Center in Japan.

We’ll keep you posted as JAXA begins testing the solar sail.

IKAROS graphic of how the sail deployed. Credit: JAXA
Posted on by Nancy Atkinson

100th Launch to the International Space Station

The Soyuz TMA-19 vehicle blasted off from Baikonur Cosmodrome in Kazakhstan today to bring three new crew members to the International Space Station. This was the 100th launch of missions in support of space station assembly, resupply and crew exchanges. The rocket lit up the early morning sky in Kazakhstan at 3:35 a.m. Wednesday local time, (5:35:19 p.m. EDT and 9:35 pm GMT on Tuesday). The Soyuz took eight and a half minutes to reach orbit, but it will take about 2 days to catch up to the ISS.
Continue reading “100th Launch to the International Space Station”

Posted on by Fraser Cain

How Did Mercury Get its Name?

Planet Mercury
Planet Mercury

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Mercury is the smallest and innermost planet in the Solar System. But here’s a question, how did Mercury get its name?

Like all the planets, Mercury is named after one of the Roman gods, which were based on the gods worshipped by the Ancient Greeks. The Roman god Mercury was the son of Maia Maiestas and Jupiter in Roman mythology, and most of his aspects were based on the Greek god Hermes.

According to mythology, Mercury was the swiftest of the gods, and the one that merchants prayed to for success in their commercial transactions. And Hermes was known as the messenger of the gods in Greek mythology. This is appropriate since Mercury is the innermost planet in the Solar System, and appears to move quickly from night to night.

Since Mercury was visible with the unaided eye, most of the ancient cultures had their own name for Mercury. The ancient Babylonians called the planet Napu, after a god in their mythology. The ancient Greeks actually thought that Mercury was two planets, and they called it Apollo when it was visible in the morning sky, and Hermes when it was seen after sunset. But in the 4th century BCE, ancient astronomers realized that the two objects were one and the same, and stuck with Hermes; becoming Mercury with the Romans.

And that’s how Mercury got its name.

We’ve written several articles about the names for the planets. Here’s an article about how Jupiter got its name, and here’s a story about the name for Saturn.

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’ve also recorded an entire episode of Astronomy Cast all about Mercury. Listen here, Episode 49: Mercury.

Posted on by Nancy Atkinson

Unusual Views of the Soyuz Rocket

'Up, up the long delirious burning blue...' View from the Soyuz flame trench by 'Astro_Wheels,' astronaut Douglas Wheelock.

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Two NASA astronauts and a Russian cosmonaut will launch to the International Space Station later today, and astronauts Douglas Wheelock has been able to get up close and personal with the Soyuz rocket that will take them there. He’s taken a few pictures of his rocket from unusual vantage points and posted them on Twitter, and is sharing his prelaunch experiences, too (@Astro_Wheels). Wheelock has big shoes to fill in the Twitter and picture-taking department, as JAXA astronaut Soichi Noguchi set a new standard in making his time on board the ISS a shared experience through images and social media. More pics below, plus a newly released video by NASA of the landing of the Soyuz that brought the Noguchi, Soyuz Commander Oleg Kotov and TJ Creamer back home. It’s a view of the landing not normally seen.

'The work goes on, the cause endures, the hope still lives, and the dream shall never die. T minus 42 hours...' Tweeted Wheelock.

For the next crew heading to the ISS, which will bring the crew size back to six at the space station, veteran cosmonaut Fyodor Yurchikhin, Wheelock and Shannon Walker are scheduled for liftoff aboard the Soyuz TMA-19 spacecraft from the Baikonur Cosmodrome in Kazakhstan at 5:35:19 p.m. EDT (9:35 pm GMT) (3:35:19 a.m. June 16 local time Kazakhstan).

Including manned and unmanned missions, this will be the 100th launch supporting space station operations since assembly began in 1998.

Posted on by Nancy Atkinson

New Worlds to Explore? Kepler Spacecraft Finds 750 Exoplanet Candidates

Artist concept of Kepler in space. Credit: NASA/JPL

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The Kepler spacecraft has found over 750 candidates for extrasolar planets, and that is just from data collected in the first 43 days of the spacecraft’s observations. “This is the biggest release of candidate planets that has ever happened,” said William Borucki, Kepler’s lead scientist. “The number of candidate planets is actually greater than all the planets that have been discovered in the last 15 years.”

This is an astounding amount of potential exoplanets from data taken during such a short period of time, however Borucki added that they expect only about 50% of these candidates to actually turn out to be planets, as some may be eclipsing binary stars or other artifacts in the data. But still, even half would be the biggest group discovery of exoplanets ever.

And the exciting part is that 706 targets from this first data set have viable exoplanet candidates with sizes from as small as Earth to around the size of Jupiter. The team says the majority have radii less than half that of Jupiter.

The Kepler team has found so many candidates, they are sharing. They will keep the top 400 candidates to verify and confirm with observations using other telescopes – with observations done by Kepler team members. And today they have released the other 350 candidates, including five potential multiple planet systems.

However, some astronomers are upset about this and think the Kepler team should release all of their findings from the first year, as is typically done with NASA data.

Kepler launched on March 6, 2009, and has been on the hunt for exoplanets. Of course, the holy grail is finding an Earth-like or Earth-sized planet, especially those in the habitable zone of stars where liquid water and possibly life might exist. In the spring of 2009 the Kepler Mission conducted high precision photometry on nearly 156,000 stars to detect the frequency and characteristics of small exoplanets. Kepler studied an area in the constellation Cygnus, looking for the small changes in light that would signal a planet passing in front of its star.

But it takes time to verify candidates and find out if they are actually exoplanets. Usually, confirming the transit of an extrasolar planet requires observations of three different transits. While NASA’s policy requires astronomers to release their data from NASA instruments in a year, the Kepler team has worked out an agreement with the space agency so they can keep a certain portion of their data until they actually have time to verify this huge amount of exoplanet data. Between launch delays of other telescopes, cloudy nights for Earth based telescopes, and viewing a part of the sky that is only visible from the ground from April until September, they haven’t had the observing time they needed to check out all their planet candidates. The extension of the deadline gives the Kepler team the time to make sure they have gone through and found all the false positives and other potential misinterpretations of the Kepler data.

Dennis Overbye in the New York Times has written an article that delves more deeply into this little controversy. What is propriety data, and what is public? It’s a tough argument either way: scientists who have put years of their life into building a spacecraft should have the time they need to verify their data. But others feel the science should be open and available, and a policy is a policy: the deadline for releasing the data is here.

Whatever your feelings on open or closed data (and the Kepler team is only getting an extra six months on just part of their data, by the way), you have to be impressed with the quantity of potential exoplanet finds. And Kepler still has at least two years left of observations.

Papers of interest:

Characteristics of Kepler Planetary Candidates Based on the First Data Set: The Majority are Found to be Neptune-Size and Smaller

Five Kepler target stars that show multiple transiting exoplanet candidates

Posted on by Nancy Atkinson

Subaru Telescope Takes Montage of Hayabusa’s Return to Earth

The composite image from 11 images, each with 5 sec exposure, spaced by 35-50 sec. The magnitude of Hayabusa is estimated to be 21 mag. Credit: Subaru Telescope Team

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The world watched and waited for the Hayabusa spacecraft to make its return to Earth on June 13, 2010 and the people of Japan — who built and launched the little spacecraft that could (and did!) — were especially hopeful in watching and waiting. Japan’s Subaru Telescope (although located on Mauna Kea in Hawaii) turned its expectant eyes towards Hayabusa and captured the spacecraft’s flight between the Moon and Earth in 11 different images.

A note from the Subaru Telescope team:

During the busy time preparing the observations, Doctor Masafumi Yagi and his team managed to maneuver the telescope just in time to catch Hayabusa before it disappeared down south in the twilight sky. At that time, Hayabusa was a little less than half way between Moon and Earth. Five seconds exposures, each spaced by 35 – 50 seconds in the V filter with Suprime Cam, it showed up in clear trace at the position expected to be. Brightness is estimated to be only 21 magnitudes. At this level, one can see a background galaxy clearly.

We are waiting to hear more from the project team at ISAS/JAXA. In the meantime, congratulations to all who are involved in this unprecedented endeavor.

A GIF animation of the 11 images is available here — but be warned, the file is huge. You can click on the top image for a full-sized huge-ified image, too.

And here are some images of the recovery teams who picked up the sample return canister in the Woomera Prohibited Area in Australia. The canister will be taken to Japan and opened in a few weeks, or perhaps months, after rigorous testing. Only then will we find out if any asteroid samples made it in the canister for the ride back to Earth.

Recovery team makes sure all is safe with the sample return canister. Credit: JAXA
The recovery team handles the heat sheild for the Hayabusa sample return capsule. Credit: JAXA, Hayabusa Twitter feed.
JAXA's Hayabusa space capsule is transported inside a box to a clean room inside the Instrumentation Building at the Woomera Test Range, South Australia. Credit: Australian Science Media Centre

You can see more images of the canister retrieval at the Hayabusa Twitpic page and the Australian Science Media Centre’s Flickr page

Source: Subaru

Posted on by Nancy Atkinson

Vast Oceans Likely Covered One Third of Mars

n illustration of what Mars might have looked like some 3.5 billion years ago when an ocean likely covered one-third of the planet’s surface, according to a new University of Colorado at Boulder study. (Illustration by University of Colorado)

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Like rising waters from a flood, the evidence for past water on Mars — and large amounts of it – keep mounting. The latest study, which combined the analysis of water-related features including scores of delta deposits and thousands of river valleys with a look at the possibility of a global hydrosphere on early Mars, found that a vast ocean likely covered one-third of the surface of Mars some 3.5 billion years ago.

“Collectively, these results support the existing theories regarding the extent and formation time of an ancient ocean on Mars,” said Gaetano Di Achille and Brian Hynek from the Univesity of Colorado at Boulder, in their article in Nature Geoscience, “and imply the surface conditions during the time probably allowed the occurrence of a global and active hydrosphere integrating valley networks, deltas and a vast ocean as major components of an Earth-like hydrologic cycle.”

The idea of an ocean on Mars has been repeatedly proposed and challenged over the past two decades, and just last week, another study proposed lakes in the Hellas Basin region on Mars. This new study provides further support for the idea of a sustained sea on the Red Planet during the Noachian era more than 3 billion years ago.

More than half of the 52 river delta deposits identified by the CU researchers — each of which was fed by numerous river valleys — likely marked the boundaries of the proposed ocean, since all were at about the same elevation. Twenty-nine of the 52 deltas were connected either to the ancient Mars ocean or to the groundwater table of the ocean and to several large, adjacent lakes, Di Achille said.

The study is the first to integrate multiple data sets of deltas, valley networks and topography from a cadre of NASA and European Space Agency orbiting missions of Mars dating back to 2001, said Hynek. The study implies that ancient Mars probably had an Earth-like global hydrological cycle, including precipitation, runoff, cloud formation, and ice and groundwater accumulation.

Di Achille and Hynek used a geographic information system, or GIS, to map the Martian terrain and conclude the ocean likely would have covered about 36 percent of the planet and contained about 30 million cubic miles, or 124 million cubic kilometers, of water. The amount of water in the ancient ocean would have formed the equivalent of a 1,800-foot, or 550-meter-deep layer of water spread out over the entire planet.
The volume of the ancient Mars ocean would have been about 10 times less than the current volume of Earth’s oceans, Hynek said. Mars is slightly more than half the size of Earth.

The average elevation of the deltas on the edges of the proposed ocean was remarkably consistent around the whole planet, said Di Achille. In addition, the large, ancient lakes upslope from the ancient Mars ocean likely formed inside impact craters and would have been filled by the transport of groundwater between the lakes and the ancient sea, according to the researchers.

A second study headed by Hynek and involving CU-Boulder researcher Michael Beach of LASP and CU-Boulder doctoral student Monica Hoke being published in the Journal of Geophysical Research–Planets — which is a publication of the American Geophysical Union — detected roughly 40,000 river valleys on Mars. That is about four times the number of river valleys that have previously been identified by scientists, said Hynek.

The river valleys were the source of the sediment that was carried downstream and dumped into the deltas adjacent to the proposed ocean, said Hynek. “The abundance of these river valleys required a significant amount of precipitation,” he said. “This effectively puts a nail in the coffin regarding the presence of past rainfall on Mars.” Hynek said an ocean was likely required for the sustained precipitation.

“One of the main questions we would like to answer is where all of the water on Mars went,” said Di Achille. He said future Mars missions — including NASA’s $485 million Mars Atmosphere and Volatile Evolution mission, or MAVEN, which is being led by CU-Boulder and is slated to launch in 2013 — should help to answer such questions and provide new insights into the history of Martian water.

The river deltas on Mars are of high interest to planetary scientists because deltas on Earth rapidly bury organic carbon and other biomarkers of life and are a prime target for future exploration. Most astrobiologists believe any present indications of life on Mars will be discovered in the form of subterranean microorganisms.
“On Earth, deltas and lakes are excellent collectors and preservers of signs of past life,” said Di Achille. “If life ever arose on Mars, deltas may be the key to unlocking Mars’ biological past.”

Hynek said long-lived oceans may have provided an environment for microbial life to take hold on Mars.

Source: CU-Boulder