Universe Today

December 3, 2014September 19, 2017 by Matt Williams

10 Interesting Facts About the Milky Way

Viewed from above, we can now see that our gaze takes across the Perseus Arm (toward the constellation Cygnus), parts of the Sagittarius and Scutum-Centaurus arms (toward the constellations Scutum, Sagittarius and Ophiuchus) and across the central bar. Interstellar dust obscures much of the center of the galaxy. Credit: NASA et. all with additions by the author.

The Milky Way Galaxy is an immense and very interesting place. Not only does it measure some 120,000–180,000 light-years in diameter, it is home to planet Earth, the birthplace of humanity. Our Solar System resides roughly 27,000 light-years away from the Galactic Center, on the inner edge of one of the spiral-shaped concentrations of gas and dust particles called the Orion Arm.

But within these facts about the Milky Way lie some additional tidbits of information, all of which are sure to impress and inspire. Here are ten such facts, listed in no particular order:

1. It’s Warped:

For starters, the Milky Way is a disk about 120,000 light years across with a central bulge that has a diameter of 12,000 light years (see the Guide to Space article for more information). The disk is far from perfectly flat though, as can be seen in the picture below. In fact, it is warped in shape, a fact which astronomers attribute to the our galaxy’s two neighbors -the Large and Small Magellanic clouds.

These two dwarf galaxies — which are part of our “Local Group” of galaxies and may be orbiting the Milky Way — are believed to have been pulling on the dark matter in our galaxy like in a game of galactic tug-of-war. The tugging creates a sort of oscillating frequency that pulls on the galaxy’s hydrogen gas, of which the Milky Way has lots of (for more information, check out How the Milky Way got its Warp).

The Spiral Galaxy ESO 510-13 is warped similar to our own. Credit: NASA/Hubble Heritage Team (STScI / AURA), C. Conselice (U. Wisconsin / STScI/ NASA — *The warp of Spiral Galaxy ESO 510-13 is similar to that of our own. Credit: NASA/Hubble*

2. It Has a Halo, but You Can’t Directly See It:

Scientists believe that 90% of our galaxy’s mass consists of dark matter, which gives it a mysterious halo. That means that all of the “luminous matter” – i.e. that which we can see with the naked eye or a telescopes – makes up less than 10% of the mass of the Milky Way. Its halo is not the conventional glowing sort we tend to think of when picturing angels or observing comets.

In this case, the halo is actually invisible, but its existence has been demonstrated by running simulations of how the Milky Way would appear without this invisible mass, and how fast the stars inside our galaxy’s disk orbit the center.

The heavier the galaxy, the faster they should be orbiting. If one were to assume that the galaxy is made up only of matter that we can see, then the rotation rate would be significantly less than what we observe. Hence, the rest of that mass must be made up of an elusive, invisible mass – aka. “dark matter” – or matter that only interacts gravitationally with “normal matter”.

To see some images of the probable distribution and density of dark matter in our galaxy, check out The Via Lactea Project.

3. It has Over 200 Billion Stars:

As galaxies go, the Milky Way is a middleweight. The largest galaxy we know of, which is designated IC 1101, has over 100 trillion stars, and other large galaxies can have as many as a trillion. Dwarf galaxies such as the aforementioned Large Magellanic Cloud have about 10 billion stars. The Milky Way has between 100-400 billion stars; but when you look up into the night sky, the most you can see from any one point on the globe is about 2,500. This number is not fixed, however, because the Milky Way is constantly losing stars through supernovae, and producing new ones all the time (about seven per year).

These images taken by the Spitzer Space Telescope show the dust and gas concentrations around a supernova. Credit: NASA/JPL-Caltech — *These images taken by the Spitzer Space Telescope show dust and gas concentrations around a distant supernova. Credit: NASA/JPL-Caltech*

4. It’s Really Dusty and Gassy:

Though it may not look like it to the casual observer, the Milky Way is full of dust and gas. This matter makes up a whopping 10-15% of the luminous/visible matter in our galaxy, with the remainder being the stars. Our galaxy is roughly 100,000 light years across, and we can only see about 6,000 light years into the disk in the visible spectrum. Still, when light pollution is not significant, the dusty ring of the Milky Way can be discerned in the night sky.

The thickness of the dust deflects visible light (as is explained here) but infrared light can pass through the dust, which makes infrared telescopes like the Spitzer Space Telescope extremely valuable tools in mapping and studying the galaxy. Spitzer can peer through the dust to give us extraordinarily clear views of what is going on at the heart of the galaxy and in star-forming regions.

5. It was Made From Other Galaxies:

The Milky Way wasn’t always as it is today – a beautiful, warped spiral. It became its current size and shape by eating up other galaxies, and is still doing so today. In fact, the Canis Major Dwarf Galaxy is the closest galaxy to the Milky Way because its stars are currently being added to the Milky Way’s disk. And our galaxy has consumed others in its long history, such as the Sagittarius Dwarf Galaxy.

6. Every Picture You’ve Seen of the Milky Way Isn’t It:

Currently, we can’t take a picture of the Milky Way from above. This is due to the fact that we are inside the galactic disk, about 26,000 light years from the galactic center. It would be like trying to take a picture of your own house from the inside. This means that any of the beautiful pictures you’ve ever seen of a spiral galaxy that is supposedly the Milky Way is either a picture of another spiral galaxy, or the rendering of a talented artist.

Artist's concept of Sagittarius A, the supermassive black hole at the center of our galaxy. Credit: NASA/JPL — *Artist’s concept of Sagittarius A, the supermassive black hole at the center of our galaxy. Credit: NASA/JPL-Caltech*

Imaging the Milky Way from above is a long, long way off. However, this doesn’t mean that we can’t take breathtaking images of the Milky Way from our vantage point!

7. There is a Black Hole at the Center:

Most larger galaxies have a supermassive black hole (SMBH) at the center, and the Milky Way is no exception. The center of our galaxy is called Sagittarius A*, a massive source of radio waves that is believed to be a black hole that measures 22,5 million kilometers (14 million miles) across – about the size of Mercury’s orbit. But this is just the black hole itself.

All of the mass trying to get into the black hole – called the accretion disk – forms a disk that has 4.6 million times the mass of our Sun and would fit inside the orbit of the Earth. Though like other black holes, Sgr A* tries to consume anything that happens to be nearby, star formation has been detected near this behemoth astronomical phenomenon.

8. It’s Almost as Old as the Universe Itself:

The most recent estimates place the age of the Universe at about 13.7 billion years. Our Milky Way has been around for about 13.6 billion of those years, give or take another 800 million. The oldest stars in our the Milky Way are found in globular clusters, and the age of our galaxy is determined by measuring the age of these stars, and then extrapolating the age of what preceded them.

Though some of the constituents of the Milky Way have been around for a long time, the disk and bulge themselves didn’t form until about 10-12 billion years ago. And that bulge may have formed earlier than the rest of the galaxy.

9. It’s Part of the Virgo Supercluster:

As big as it is, the Milky Way is part of an even larger galactic structures. Our closest neighbors include the Large and Small Magellanic Clouds, and the Andromeda Galaxy – the closest spiral galaxy to the Milky Way. Along with some 50 other galaxies, the Milky Way and its immediate surroundings make up a cluster known as the Local Group.

*A mosaic of telescopic images showing the galaxies of the Virgo Supercluster. Credit: NASA/Rogelio Bernal Andreo*

And yet, this is still just a small fraction of our stellar neighborhood. Farther out, we find that the Milky Way is part of an even larger grouping of galaxies known as the Virgo Supercluster. Superclusters are groupings of galaxies on very large scales that measure in the hundreds of millions of light years in diameter. In between these superclusters are large stretches of open space where intrepid explorers or space probes would encounter very little in the way of galaxies or matter.

In the case of the Virgo Supercluster, at least 100 galaxy groups and clusters are located within it massive 33 megaparsec (110 million light-year) diameter. And a 2014 study indicates that the Virgo Supercluster is only a lobe of a greater supercluster, Laniakea, which is centered on the Great Attractor.

10. It’s on the move:

The Milky Way, along with everything else in the Universe, is moving through space. The Earth moves around the Sun, the Sun around the Milky Way, and the Milky Way as part of the Local Group, which is moving relative to the Cosmic Microwave Background (CMB) radiation – the radiation left over from the Big Bang.

The CMB is a convenient reference point to use when determining the velocity of things in the universe. Relative to the CMB, the Local Group is calculated to be moving at a speed of about 600 km/s, which works out to about 2.2 million km/h. Such speeds stagger the mind and squash any notions of moving fast within our humble, terrestrial frame of reference!

We have written many interesting articles about the Milky Way for Universe Today. Here’s 10 Interesting Facts about the Milky Way, How Big is the Milky Way?, What is the Closest Galaxy to the Milky Way?, and How Many Stars Are There in the Milky Way?

For many more facts about the Milky Way, visit the Guide to Space, listen to the Astronomy Cast episode on the Milky Way, or visit the Students for the Exploration and Development of Space at seds.org.

December 3, 2014December 23, 2015 by Matt Williams

Meteorite May Contain Proof of Life on Mars, Researchers Say

The idea that Mars could have supported life at one time is the subject of ongoing debate. Image credit: NASA

Mars is currently home to a small army robotic rovers, satellites and orbiters, all of which are busy at work trying to unravel the deeper mysteries of Earth’s neighbor. These include whether or not the planet ever had liquid water on its surface, what the atmosphere once looked like, and – most importantly of all – if it ever supported life.

And while much has been learned about Martian water and its atmosphere, the all-important question of life remains unanswered. Until such time as organic molecules – considered to be the holy grail for missions like Curiosity – are found, scientists must look elsewhere to find evidence of Martian life.

According to a recent paper submitted by an international team of scientists, that evidence may have arrived on Earth three and a half years ago aboard a meteorite that fell in the Moroccan desert. Believed to have broken away from Mars 700,000 years ago, so-called Tissint meteorite has internal features that researchers say appear to be organic materials.

The paper appeared in the scientific journal Meteoritics and Planetary Sciences. In it, the research team – which includes scientists from the Swiss Federal Institute of Technology in Lausanne (EPFL) – indicate organic carbon is located inside fissures in the rock. All indications are the meteorite is Martian in origin.

“So far, there is no other theory that we find more compelling,” says Philippe Gillet, director of EPFL’s Earth and Planetary Sciences Laboratory. He and his colleagues from China, Japan and Germany performed a detailed analysis of organic carbon traces from a Martian meteorite, and have concluded that they have a very probable biological origin.

Artist's conception of an fragment as it blasts off from Mars. Boulder-sized planetary fragments could be a mechanism that carried life between Mars and Earth, UA planetary scientist Jay Melosh says. (Credit: The Planetary Society) — *Artist’s conception of an fragment as it blasts off from Mars as a result of a meteor impact. Credit: The Planetary Society*

The scientists argue that carbon could have been deposited into the fissures of the rock when it was still on Mars by the infiltration of fluid that was rich in organic matter.

If this sounds familiar, you may recall a previous Martian meteorite named ALH84001, found in the Allen Hills region in Antarctica. In 1996 NASA researchers announced they had found evidence within ALH84001 that strongly suggested primitive life may have existed on Mars more than 3.6 billion years ago. While subsequent studies of the now famous Allen Hills Meteorite shot down theories that the Mars rock held fossilized alien life, both sides continue to debate the issue.

This new research on the Tissint meteorite will likely be reviewed and rebutted, as well.

The researchers say the meteorite was likely ejected from Mars after an asteroid crashed on its surface, and fell to Earth on July 18, 2011, and fell in Morocco in view of several eyewitnesses.

Upon examination, the alien rock was found to have small fissures that were filled with carbon-containing matter. Several research teams have already shown that this component is organic in nature, but they are still debating where the carbon came from.

Chemical, microscopic and isotope analysis of the carbon material led the researchers to several possible explanations of its origin. They established characteristics that unequivocally excluded a terrestrial origin, and showed that the carbon content were deposited in the Tissint’s fissures before it left Mars.

This research challenges research proposed in 2012 that asserted that the carbon traces originated through the high-temperature crystallization of magma. According to the new study, a more likely explanation is that liquids containing organic compounds of biological origin infiltrated Tissint’s “mother” rock at low temperatures, near the Martian surface.

A piece of the Tissint meteorite that came to Earth via Mars. Credit: EPFL/Alain Herzog — *A piece of the Tissint meteorite that landed on Earth on July 18th, 2011. Credit: EPFL/Alain Herzog*

These conclusions are supported by several intrinsic properties of the meteorite’s carbon, e.g. its ratio of carbon-13 to carbon-12. This was found to be significantly lower than the ratio of carbon-13 in the CO2 of Mars’s atmosphere, previously measured by the Phoenix and Curiosity rovers.

Moreover, the difference between these ratios corresponds perfectly with what is observed on Earth between a piece of coal – which is biological in origin – and the carbon in the atmosphere.

The researchers note that this organic matter could also have been brought to Mars when very primitive meteorites – carbonated chondrites – fell on it. However, they consider this scenario unlikely because such meteorites contain very low concentrations of organic matter.

“Insisting on certainty is unwise, particularly on such a sensitive topic,” warns Gillet. “I’m completely open to the possibility that other studies might contradict our findings. However, our conclusions are such that they will rekindle the debate as to the possible existence of biological activity on Mars – at least in the past.”

Be sure to check out these videos from EPFL News, which include an interview with Philippe Gillet, EPFL and co-author of the study:

And this video explaining the history of the Tissint meteor:

Further Reading: EPFL

December 3, 2014December 23, 2015 by Ken Kremer

T Minus 1 Day to Launch: Orion at the Pad Photos

Orion spacecraft atop Delta 4 Heavy rocket Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida one day prior to launch set for Dec. 4, 2014. Credit: Ken Kremer - kenkremer.com

KENNEDY SPACE CENTER, FL – The debut blastoff of NASA’s new Orion capsule is less than 24 hours away.

Today, Dec 3, the media including myself visited Orion and its Delta IV Heavy booster rocket for an up close look at its launch pad along the Florida space coast and set up our sound activated launch pad cameras. Enjoy my photo gallery herein.

The Orion capsule is designed to carry astronauts farther into space than ever before and open a new era in human spaceflight.

NASA’s first Orion spacecraft atop Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida one day prior to launch set for Dec. 4, 2014. Credit: Ken Kremer - kenkremer.com — NASA’s first Orion spacecraft atop Delta 4 Heavy Booster at Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida one day prior to launch set for Dec. 4, 2014. Credit: Ken Kremer – kenkremer.com

Tens of thousands of visitors have flocked to the space coast. Area hotels have been sold out for many weeks. Huge crowds are expected for perhaps the biggest crowd of spectators for any launch since the space shuttles were retired in July 2011.

Orion is slated to lift off on a United Launch Alliance Delta IV Heavy rocket on its inaugural test flight to space on the uncrewed Exploration Flight Test-1 (EFT-1) mission at 7:05 a.m. EST on December 4, 2014 from Space Launch Complex 37 (SLC-37) at Cape Canaveral Air Force Station in Florida.

Up close view of Orion inside the mobile service tower pad 37 at Cape Canaveral Air Force Station in Florida one day prior to launch. Credit: Ken Kremer - kenkremer.com — Up close view of Orion inside the mobile service tower pad 37 at Cape Canaveral Air Force Station in Florida one day prior to launch. Credit: Ken Kremer – kenkremer.com

The weather forecast has improved from 60% to 70% chance of GO, with favorable conditions at expected at launch time at 7:05 a.m. on Dec. 4, 2014.

The launch window extends for 2 hours and 39 minutes.
.
The two-orbit, four and a half hour Orion EFT-1 flight around Earth will lift the Orion spacecraft and its attached second stage to an orbital altitude of 3,600 miles, about 15 times higher than the International Space Station (ISS) – and farther than any human spacecraft has journeyed in 40 years.

NASA TV will provide several hours of live Orion EFT-1 launch coverage with the new countdown clock – starting at 4:30 a.m. on Dec. 4.

Watch for Ken’s ongoing Orion coverage and he is onsite at KSC in the days leading up to the historic launch on Dec. 4.

Stay tuned here for Ken’s continuing Orion and Earth and planetary science and human spaceflight news.

Ken Kremer

………….

Learn more about Orion, SpaceX, Antares, NASA missions and more at Ken’s upcoming outreach events:

Dec 1-5: “Orion EFT-1, SpaceX CRS-5, Antares Orb-3 launch, Curiosity Explores Mars,” Kennedy Space Center Quality Inn, Titusville, FL, evenings

December 3, 2014December 23, 2015 by David Dickinson

Rise of the Mega Rockets: Comparing Heavy Lift Launch Systems

An Ariane 5 heads spaceward. Credit: Ariane.tv screenshot.

A new generation of space rockets ready to lift new and exciting payloads spaceward is coming to a sky near you.

Tomorrow, a Delta IV Heavy rocket will boost the Orion space capsule on a two orbit journey around the Earth that will test key systems. And though tomorrow’s launch is uncrewed, the Orion Command Module will one day form the core of NASA’s Orion MPCV Multi-Purpose Crew Vehicle and is slated to care out humanity’s first mission to an asteroid and beyond in the next decade.

But a second, lesser known launch also leaves Earth tomorrow as well, atop a rocket that will soon give way to a new generation of lift boosters as launch services vie for new customers. Just over eight hours after the launch of EFT-1, an Ariane 5 rocket lifts off from French Guiana with GSAT-16.

Credit Jason Major. — The EFT-1 Delta IV Heavy posed for roll out. Credit: Jason Major. @JPMajor

Is the ‘battle of the boosters’ heating up?

This comes after the December 2^nd announcement earlier this week by participating members of the European Space Agency to proceed with the development of the next generation Ariane 6 rocket. Also included in the 5.9 billion Euro (7.3 billion USD) budget proposal is funding for the 2018 ExoMars mission, along with further support of ESA’s International Space Station commitments.

To date, ESA has fielded five of its Automated Transfer cargo Vehicles (ATVs) on missions to the International Space Station. ESA will also design the Service Module segment of the Orion MPCV.

“I can summarize this ministerial council by say it was a success… I’d even go so far as to say that it is a great success,” said Jean-Jacques Dordain, the director-general of the European Space Agency.

The Ariane 6 is expected to be on the launch pad by 2020, and will feature two variants capable of placing 5 to 11 tonnes in a geostationary transfer orbit. The solid fuel booster to be incorporated will be based on the Vega rocket design, while the upper stage Vinci engine is already currently in development.

Ariane 6. Credit Wikimedia Commons, SkywalkerPL. — A look at the Ariane 6 rocket. Credit Wikimedia Commons, SkywalkerPL.

The design has been hotly contested among European Space Agency members, many of whom are in favor of other variants based on the upgraded Ariane 5. Some of the largest rockets of all time included those developed by NPO Energia, capable of lofting 100,000 kilograms into low Earth orbit. An Energia N1 Moon rocket exploded on the pad on July 3^rd 1969, effectively ending the Soviet Union’s bid to put a man on the Moon. In comparison, the massive Saturn V rocket — thus far, the largest and most powerful ever fielded by the United States — could deploy the equivalent of 118,000 kg to low Earth orbit and 47,000 kg to a Trans-Lunar Insertion orbit around the Moon.

But that’s just the beginning. Though the Orion capsule will ride atop a United Launch Services Delta IV Heavy tomorrow — a system usually employed for launching clandestine spy satellites — NASA hopes to have its own Space Launch System (SLS) rocket sitting on the pad by the end of 2018. Boeing was awarded the contract for SLS earlier this year, and the system largely rose re-imagined from the ashes of the cancelled Constellation program. The SLS Block 1 is expected to have a lift capacity of 70,000 kg to LEO, while Boeing’s proposed SLS Block 2 variant would, if fielded, have the largest lift capacity of all time at 130,000 kg to LEO. Only the Long March 9 proposed by China approaches that lofty goal.

An artist’s concept of Orion headed towards deep space. Credit: NASA.

And the wild card is Elon Musk’s SpaceX. Already in the game of sending cargo via its Dragon spacecraft to the ISS, SpaceX is developing a reputation for dependability when it comes to getting satellites into orbit at relatively low cost. SpaceX hopes to field its Falcon 9 Heavy with a lift capacity of 53,000 kg to LEO sometime in 2015, and many proposed missions are banking on the the Falcon 9 Heavy as a future service provider for solar system exploration. Certainly, with the recent failure of the Antares rocket on October 28th, SpaceX may look like the more attractive option to many, and the development of the Ariane 6 is expected to face stiff competition in the brave new world of high tech rocketry.

Ever wonder what all of these launch vehicles and spacecraft past and present look like stacked up against each other? There’s a graphic for that, recently featured on Io9:

Credit: Heaney555 — A breakdown and comparison of spacecraft launch systems. Click to enlarge. Credit: Reddit user Heaney555.

From Almaz to Zarya, this is a fascinating study in scale comparison. Be sure to zoom in and check out the tiny ant-like crew compliment of each, also to scale. Of course, the backyard satellite-tracker in us can’t help be notice the brightness-versus size comparison for many of these. For example, the International Space Station on a good pass can appear as bright as Venus at -4^th magnitude — and even look “TIE Fighter shaped” in binoculars — while the smaller Shenzhou and Soyuz modules are often barely visible as they pass overhead. And how we miss watching the Shuttle paired with the International Space Station as they both glided silently by:

But such orbital drama can still be caught if you know when and where to look for it. And speaking of which, viewers in western Australia and the southwestern United States may be able to see Orion and EFT-1 on its first lap around the Earth tomorrow before it fires its engines over the Atlantic headed for a 5,800 km apogee over southern Africa. Assuming EFT-1 lifts off at the beginning of its 159 minute launch window at 7:05 AM EST/12:05 UT, expect it to see it crossing dusk skies over western Australia at 55 minutes after liftoff, and dawn skies for the southwestern U.S. at 95 minutes post-launch respectively.

An awesome sight to behold indeed, marking the start of a brave new era of space exploration.

So what do you, the astute and space-minded reader of Universe Today think? Are the SLS and its kin the lift vehicle(s) of the future, or ‘rockets to nowhere?’ Will they survive the political winds that are bound to blow over the coming decade? Will the Ariane 6 best the Falcon 9 as the lift platform of choice?

One thing is for sure, expect coverage of space exploration drama and more to continue here at Universe Today!

December 3, 2014December 23, 2015 by Bob King

Soar with the Aurora in this Breathtaking Real-time Video

Scene from "Soaring". Credit: Ole Salomonsen

“Soaring” by Ole Salomonsen

We’ve posted many beautiful aurora photos and videos over the years here at Universe Today, but this one about stopped my heart. Titled “Soaring”, it was all shot in real time by Ole Salomonsen, a landscape photographer based in Tromsø, Norway. Salomonsen has been shooting spectacular stills and videos of the northern lights for years. While not the first aurora video done in real time, it’s probably the most successful, high definition effort to date. Ole used a Sony A7S, which he calls “the best low light camera ever”.

It was shot from late August to mid-November in and around the city of Tromsø, as well as on the island of Senja, Norway’s second largest island and a three-hour drive from the city. But what sets this video apart from many is that it shows the aurora unfolding live as if you’re standing right there. No time lapse.

Coronal aurora scene from "Soaring". Credit: Ole Salomonsen — *Coronal aurora scene from “Soaring”. Credit: Ole Salomonsen*

Having witnessed the northern lights many times over the years from my home in northern Minnesota, I can vouch for how close to reality this work truly is. There’s a little more color saturation than what the naked eye would pick up, but the aurora’s changing rhythms are beautifully captured. Ole also mixes in dramatic pan shots taken as if you were running to find a clearing to get the best view. Honestly, that blew me away.

“Although auroras mostly move slowly and majestic, they can also move really fast,” wrote Salomonsen. After seeing the slow undulations of curtains and rays early in the film, you’ll really appreciate the aurora’s other side – its dazzling speed.

“The corona I captured and the lightning fast sequences at the end are some of the most amazing shows I have witnessed in my many years of hunting and filming the lights,” added Ole.

And now for the most amazing part. What you just watched is only a fraction of what Salomonsen has shot during the season. Expect more soon!

December 3, 2014June 25, 2016 by Matt Williams

The Inner Planets of Our Solar System

The terrestrial planets of our Solar System at approximately relative sizes. From left, Mercury, Venus, Earth and Mars. Credit: Lunar and Planetary Institute

Our Solar System is an immense and amazing place. Between its eight planets, 176 moons, 5 dwarf planets (possibly hundreds more), 659,212 known asteroids, and 3,296 known comets, it has wonders to sate the most demanding of curiosities. Our Solar System is made up of different regions, which are delineated based on their distance from the Sun, but also the types of planets and bodies that can be found within them.

In the inner Solar System, we find the “Inner Planets” – Mercury, Venus, Earth, and Mars – which are so named because they orbit closest to the Sun. In addition to their proximity, these planets have a number of key differences that set them apart from planets elsewhere in the Solar System.

For starters, the inner planets are rocky and terrestrial, composed mostly of silicates and metals, whereas the outer planets are gas giants. The inner planets are also much more closely spaced than their outer Solar System counterparts. In fact, the radius of the entire region is less than the distance between the orbits of Jupiter and Saturn.

The positions and names of planets and dwarf planets in the solar system. Credit: Planets2008/Wikimedia Commons — *The positions and names of planets and dwarf planets in the solar system.*
*Credit: Planets2008/Wikimedia Commons*

This region is also within the “frost line,” which is a little less than 5 AU (about 700 million km) from the Sun. This line represents the boundary in a system where conditions are warm enough that hydrogen compounds such as water, ammonia, and methane are able to take liquid form. Beyond the frost line, these compounds condense into ice grains.Some scientists refer to the frost line as the “Goldilocks Zone” — where conditions for life may be “just right.”

Generally, inner planets are smaller and denser than their counterparts, and have few to no moons or rings circling them. The outer planets, meanwhile, often have dozens of satellites and rings composed of particles of ice and rock.

The terrestrial inner planets are composed largely of refractory minerals, such as the silicates, which form their crusts and mantles, and metals such as iron and nickel which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather. All of them have impact craters and tectonic surface features as well, such as rift valleys and volcanoes.

Mercury:

Of the inner planets, Mercury is the closest to our Sun and the smallest of the terrestrial planets. This small planet looks very much like the Earth’s Moon and is even a similar grayish color, and it even has many deep craters and is covered by a thin layer of tiny particle silicates.

Its magnetic field is only about 1 percent that of Earth’s, and it’s very thin atmosphere means that it is hot during the day (up to 430°C) and freezing at night (as low as -187 °C) because the atmosphere can neither keep heat in or out. It has no moons of its own and is comprised mostly of iron and nickel. Mercury is one of the densest planets in the Solar System.

Venus:

Venus, which is about the same size as Earth, has a thick toxic atmosphere that traps heat, making it the hottest planet in the Solar System. This atmosphere is composed of 96% carbon dioxide, along with nitrogen and a few other gases. Dense clouds within Venus’ atmosphere are composed of sulphuric acid and other corrosive compounds, with very litter water.

Only two spacecraft have ever penetrated Venus’s thick atmosphere, but it’s not just man-made objects that have trouble getting through. There are fewer crater impacts on Venus than other planets because all but the largest meteors don’t make it through the thick air without disintegrating. Much of Venus’ surface is marked with volcanoes and deep canyons — the biggest of which is over 6400 km (4,000 mi) long.

Venus is often called the “morning star” because, with the exception of Earth’s moon, it’s the brightest object we see in the sky. Like Mercury, Venus has no moon of its own.

Earth:

Earth is the third inner planet and the one we know best. Of the four terrestrial planets, Earth is the largest, and the only one that currently has liquid water, which is necessary for life as we know it. Earth’s atmosphere protects the planet from dangerous radiation and helps keep valuable sunlight and warmth in, which is also essential for life to survive.

Inner Solar System. Image credit: NASA — *Illustration of the Inner Planets and their orbits around the Sun Image credit: NASA*

Like the other terrestrial planets, Earth has a rocky surface with mountains and canyons, and a heavy metal core. Earth’s atmosphere contains water vapor, which helps to moderate daily temperatures. Like Mercury, the Earth has an internal magnetic field. And our Moon, the only one we have, is comprised of a mixture of various rocks and minerals.

Mars:

Mars is the fourth and final inner planet, and also known as the “Red Planet” due to the rust of iron-rich materials that form the planet’s surface. Mars also has some of the most interesting terrain features of any of the terrestrial planets. These include the largest mountain in the Solar System – Olympus Mons – which rises some 21,229 m (69,649 ft) above the surface, and a giant canyon called Valles Marineris. Valles Marineris is 4000 km (2500 mi) long and reaches depths of up to 7 km (4 mi)!

For comparison, the Grand Canyon in Arizona is about 800 km (500 mi) long and 1.6 km (1 mi) deep. In fact, the extent of Valles Marineris is as long as the United States and it spans about 20 percent (1/5) of the entire distance around Mars. Much of the surface is very old and filled with craters, but there are geologically newer areas of the planet as well.

A top-down image of the orbits of Earth and Mars. Image: NASA — *A top-down image of the orbits of Earth and Mars. Credit: NASA*

At the Martian poles are polar ice caps that shrink in size during the Martian spring and summer. Mars is less dense than Earth and has a smaller magnetic field, which is indicative of a solid core, rather than a liquid one.

Mars’ thin atmosphere has led some astronomers to believe that the surface water that once existed there might have actually taken liquid form, but has since evaporated into space. The planet has two small moons called Phobos and Deimos.

Beyond Mars are the four outer planets: Jupiter, Saturn, Uranus, and Neptune.

We have written many interesting articles about the inner planets here at Universe Today. Here’s The Solar System Guide as well as The Inner and Outer Planets in Our Solar System.

For more information, check out this article from NASA on the planets of the Solar System and this article from Solstation about the inner planets.

Astronomy Cast also has episodes on all of the inner planets including this one about Mercury.

December 3, 2014December 23, 2015 by Nancy Atkinson

Japan Successfully Launches Hayabusa 2 Asteroid Sample Return Mission

The Hayabusa 2 spacecraft. Credit: JAXA.

Japan successfully launched their Hayabusa-2 sample return mission to asteroid 1999 JU3, and JAXA reports the spacecraft is on course and in excellent shape, with its solar panels deployed. The H-IIA F26 rocket carrying the craft blasted off from the Tanegashima Space Center in southwest Japan at 1:22:04 p.m. local time on Dec 3, 2014 (04:22 UTC) , and about two hours later, the spacecraft separated from the rocket and entered its initial planned trajectory.

Hayabusa 2 has been communicating with JAXA mission control as it starts off on its journey to land on an asteroid in 2018 and retrieve rock and dust samples to be returned to Earth in late 2020.

The first Hayabusa spacecraft completed a successful — albeit nail-biting — mission to the asteroid Itokawa, returning samples to Earth in 2010 after first reaching the asteroid in 2005. The mission almost failed as the spacecraft was plagued by technical problems and it wasn’t certain if the mechanism used to capture the samples actually worked. Ultimately, after a circuitous and troubled-filled return trip home, the canister containing microscopic rock samples made a soft landing in Australia, the first time that samples from an asteroid had been brought back to Earth for study.

Hayabusa 2’s target, Asteroid 1999 JU3 is approximately 914 meters (3,000 feet) in diameter, a little larger than Itokawa, and is roughly spherical in shape, while Itokawa had an oblong shape. 1999 JU3 has a rotation period of approximately 7.6 hours.

Relative size of Asteroid 1999 JU3. pic.twitter.com/lIHXVasJoY

— Ron Baalke (@RonBaalke) December 3, 2014

To avoid a repetition of the glitches experienced by the first Hayabusa spacecraft, JAXA made several changes. Hayabusa 2 has an updated ion propulsion engine as well as improved guidance and navigation systems, new antennas and a new altitude control system.

Hayabusa 2 has a mini rover called Minerva 2, and for Hayabusa 2’s sample-collecting activities, a slowly descending impactor will be used, detonating upon contact with the surface instead of the high-speed projectile used by the first Hayabusa.

This video explains the Hayabusa 2 mission and how it differs from the first Hayabusa spacecraft:

JAXA’s Hayabusa website will provide current updates to the mission.

December 3, 2014December 23, 2015 by Elizabeth Howell

Mars Needs You! Help Scientists Track Spring Thaw On Red Planet

Carbon dioxide ice begins to feel the heat in the south pole region every spring. In this image of 'Inca City' taken in August 2014, you can see a few fans coming out from channels (araneiforms) that are created when pressurized gas escapes from the melting ice. Picture taken by the Mars Reconnaissance Orbiter's HiRISE camera. Credit: NASA/JPL/University of Arizona

We’ve been watching Mars with spacecraft for about 50 years, but there’s still so little we know about the Red Planet. Take this sequence of images in this post recently taken by a powerful camera on NASA’s Mars Reconnaissance Orbiter. Spring arrives in the southern hemisphere and produces a bunch of mysteries, such as gray-blue streaks you can see in a picture below.

That’s where citizen scientists can come in, according to a recent post for the University of Arizona’s High Resolution Imaging Science Experiment (HiRISE) camera that took these pictures. They’re asking people with a little spare time to sign up for Planet Four (a Zooniverse project) to look at mysterious Mars features. With amateurs and professionals working together, maybe we’ll learn more about these strange changes you see below.

On Aug. 20, 2014, Martian dust mounds are on top of the araneiforms in 'Inca City', as well as dark areas on the terrain showing where the ice cap in the southern hemisphere burst and sent gas and dust into the surroundings. Fans in the area are pointing in multiple directions, showing how the wind has changed. Image taken by the Mars Reconnaissance Orbiter's HiRISE camera. Credit: NASA/JPL/University of Arizona — On Aug. 20, 2014, Martian dust mounds are on top of the araneiforms in ‘Inca City’, as well as dark areas on the terrain showing where the ice cap in the southern hemisphere burst and sent gas and dust into the surroundings. Fans in the area are pointing in multiple directions, showing how the wind has changed. Image taken by the Mars Reconnaissance Orbiter’s HiRISE camera. Credit: NASA/JPL/University of Arizona

On Aug. 25, 2014, more fans and blotches appear on the Martian landscape around "Inca City", a location in the southern polar region, as the ice bursts in the springtime sun. Image obtained by the Mars Reconnaissance Orbiter's HiRISE camera. Credit: NASA/JPL/University of Arizona — On Aug. 25, 2014, more fans and blotches appear on the Martian landscape around “Inca City”, a location in the southern polar region, as the ice bursts in the springtime sun. Image obtained by the Mars Reconnaissance Orbiter’s HiRISE camera. Credit: NASA/JPL/University of Arizona

As of Sept. 6, 2014, fans in "Inca City" in the Martian southern hemisphere are now blue-gray. Why this color appears in the spring is unknown. It could be because of particles falling into ice underneath, or gas bursting from the ice condensing and falling as frost. It could even be a combination of the two. Image taken by the Mars Reconnaissance Orbiter's HiRISE orbiter. Credit: NASA/JPL/University of Arizona — As of Sept. 6, 2014, fans in “Inca City” in the Martian southern hemisphere are now blue-gray. Why this color appears in the spring is unknown. It could be because of particles falling into ice underneath, or gas bursting from the ice condensing and falling as frost. It could even be a combination of the two. Image taken by the Mars Reconnaissance Orbiter’s HiRISE orbiter. Credit: NASA/JPL/University of Arizona

As spring takes hold in the southern polar region of Mars on Sept. 27, 2014, cracks are now developing in the ice at "Inca City" with multiple new dust fans appearing. Cracks develop when the ice does not have a path to easily rupture and release gas. Picture taken by the Mars Reconnaissance Orbiter's HiRISE camera. Credit: NASA/JPL/University of Arizona — As spring takes hold in the southern polar region of Mars on Sept. 27, 2014, cracks are now developing in the ice at “Inca City” with multiple new dust fans appearing. Cracks develop when the ice does not have a path to easily rupture and release gas. Picture taken by the Mars Reconnaissance Orbiter’s HiRISE camera. Credit: NASA/JPL/University of Arizona

December 3, 2014November 29, 2019 by Matt Williams

Planets Could Travel Along with Rogue ‘Hypervelocity’ Stars, Spreading Life Throughout the Universe

An artist's conception of a hypervelocity star that has escaped the Milky Way. Credit: NASA

Back in 1988, astronomer Jack Hills predicted a type of “rogue”star might exist that is not bound to any particular galaxy. These stars, he reasoned, were periodically ejected from their host galaxy by some sort of mechanism to begin traveling through interstellar space.

Since that time, astronomers have made numerous discoveries that indicate these rogue, traveling stars indeed do exist, and far from being an occasional phenomenon, they are actually quite common. What’s more, some of these stars were found to be traveling at extremely high speeds, leading to the designation of hypervelocity stars (HVS).

And now, in a series of papers that published in arXiv Astrophysics, two Harvard researchers have argued that some of these stars may be traveling close to the speed of light. Known as semi-relativistic hypervelocity stars (SHS), these fast-movers are apparently caused by galactic mergers, where the gravitational effect is so strong that it fling stars out of a galaxy entirely. These stars, the researchers say, may have the potential to spread life throughout the Universe.

This finding comes on the heels of two other major announcements. The first occurred in early November when a paper published in the Astrophysical Journal reported that as many as 200 billion rogue stars have been detected in a cluster of galaxies some 4 billion light years away. These observations were made by the Hubble Space Telescope’s Frontier Fields program, which made ultra-deep multiwavelength observations of the Abell 2744 galaxy cluster.

This was followed by a study published in Science, where an international team of astronomers claimed that as many as half the stars in the entire universe live outside of galaxies.

Using ESO's Very Large Telescope, astronomers have recorded a massive star moving at more than 2.6 million kilometres per hour. Stars are not born with such large velocities. Its position in the sky leads to the suggestion that the star was kicked out from the Large Magellanic Cloud, providing indirect evidence for a massive black hole in the Milky Way's closest neighbour. Credit: ESO — *Image of a moving star captured by the ESO Very Large Telescope, believed to have been ejected from the Large Magellanic Cloud. Credit: ESO*

However, the recent observations made by Abraham Loeb and James Guillochon of Harvard University are arguably the most significant yet concerning these rogue celestial bodies. According to their research papers, these stars may also play a role in spreading life beyond the boundaries of their host galaxies.

In their first paper, the researchers trace these stars to galaxy mergers, which presumably lead to the formation of massive black hole binaries in their centers. According to their calculations, these supermassive black holes (SMBH) will occasionally slingshot stars to semi-relativistic speeds.

“We predict the existence of a new population of stars coasting through the Universe at nearly the speed of light,” Loeb told Universe Today via email. “The stars are ejected by slingshots made of pairs of massive black holes which form during mergers of galaxies.”

These findings have further reinforced that massive compact bodies, widely known as a supermassive black holes (SMBH), exist at the center of galaxies. Here, the fastest known stars exist, orbiting the SMBH and accelerating up to speeds of 10,000 km per second (3 percent the speed of light).

According to Leob and Guillochon, however, those that are ejected as a result of galactic mergers are accelerated to anywhere from one-tenth to one-third the speed of light (roughly 30,000 – 100,000 km per second).

Image of a hypervelocity star found in data from the Sloan Digital Sky Survey. Credit: Vanderbilt University

Observing these semi-relativistic stars could tell us much about the distant cosmos, according to the Harvard researchers. Compared to conventional research, which relied on subatomic particles like photons, neutrinos, and cosmic rays from distant galaxies, studying ejected stars offers numerous advantages.

“Traditionally, cosmologists used light to study the Universe but objects moving less than the speed of light offer new possibilities,” said Loeb. “For example, stars moving at different speeds allow us to probe a distant source galaxy at different look-back times (since they must have been ejected at different times in order to reach us today), in difference from photons that give us just one snapshot of the galaxy.”

In their second paper, the researchers calculate that there are roughly a trillion of these stars out there to be studied. And given that these stars were detected thanks to the Spitzer Space Telescope, it is likely that future generations will be able to study them using more advanced equipment.

All-sky infrared surveys could locate thousands of these stars speeding through the cosmos. And spectrographic analysis could tell us much about the galaxies they came from.

But how could these fast moving stars be capable of spreading life throughout the cosmos?

Could an alien spore really travel light years between different star systems? Well, as long as your theory doesn't require it to still be alive when it arrives - sure it can. — *The Theory of Panspermia argues that life is distributed throughout the universe by celestial objects. Credit: NASA/Jenny Mottar*

“Tightly bound planets can join the stars for the ride,” said Loeb. “The fastest stars traverse billions of light years through the universe, offering a thrilling cosmic journey for extra-terrestrial civilizations. In the past, astronomers considered the possibility of transferring life between planets within the solar system and maybe through our Milky Way galaxy. But this newly predicted population of stars can transport life between galaxies across the entire universe.”

The possibility that traveling stars and planets could have been responsible for the spread of life throughout the universe is likely to have implications as a potential addition to the Theory of Panspermia, which states that life exists throughout the universe and is spread by meteorites, comets, asteroids.

But Loeb told Universe Today that a traveling planetary system could have potential uses for our species someday.

“Our descendants might contemplate boarding a related planetary system once the Milky Way will merge with its sister galaxy, Andromeda, in a few billion years,” he said.

Further Reading: arxiv.org/1411.5022, arxiv.org/1411.5030

December 3, 2014December 23, 2015 by Elizabeth Howell

Europa Life: Could ‘Extreme Shrimp’ Point To Microbes On That Moon?

This is a type of shrimp that lives in hydrothermal vents (areas of hot water) in the Caribbean. NASA is studying Rimicaris hybisae and other "extreme shrimp" to learn more about lifeforms that could survive on other worlds. Credit: Chris German, WHOI/NSF, NASA/ROV Jason C: 2012 Woods

For all of the talk about aliens that we see in science fiction, the reality is in our Solar System, any extraterrestrial life is likely to be microbial. The lucky thing for us is there are an abundance of places that we can search for them — not least Europa, an icy moon of Jupiter believed to harbor a global ocean and that NASA wants to visit fairly soon. What lurks in those waters?

To gain a better understanding of the extremes of life, scientists regularly look at bacteria and other lifeforms here on Earth that can make their living in hazardous spots. One recent line of research involves shrimp that live in almost the same area as bacteria that survive in vents of up to 750 degrees Fahrenheit (400 degrees Celsius) — way beyond the boiling point, but still hospitable to life.

Far from sunlight, the bacteria receive their energy from chemical combinations (specifically, hydrogen sulfide). While the shrimp certainly don’t live in these hostile areas, they perch just at the edge — about an inch away. The shrimp feed on the bacteria, which in turn feed on the hydrogen sulfide (which is toxic to larger organisms if there is enough of it.) Oh, and by the way, some of the shrimps are likely cannibals!

One species called Rimicaris hybisae, according to the evidence, likely feeds on each other. This happens in areas where the bacteria are not as abundant and the organisms need to find some food to survive. To be sure, nobody saw the shrimps munching on each other, but scientists did find small crustaceans inside them — and there are few other types of crustaceans in the area.

But how likely, really, are these organisms on Europa? Bacteria might be plausible, but something larger and more complicated? The researchers say this all depends on how much energy the ecosystems have to offer. And in order to see up close, we’d have to get underwater somehow and do some exploring.

In a recent Universe Today interview with Mike Brown, a professor of planetary science at the California Institute of Technology, the renowned dwarf-planet hunter talked about how a submarine could do some neat work.

“In the proposed missions that I’ve heard, and in the only one that seems semi-viable, you land on the surface with basically a big nuclear pile, and you melt your way down through the ice and eventually you get down into the water,” he said. “Then you set your robotic submarine free and it goes around and swims with the big Europa whales.” You can see the rest of that interview here.

Source: Jet Propulsion Laboratory