Universe Today

October 22, 2016October 23, 2016 by Matt Williams

What is a Magnetic Field?

The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. Credit: ESA/ATG medialab

Everyone knows just how fun magnets can be. As a child, who among us didn’t love to see if we could make our silverware stick together? And how about those little magnetic rocks that we could arrange to form just about any shape because they stuck together? Well, magnetism is not just an endless source of fun or good for scientific experiments; it’s also one of basic physical laws upon which the universe is based.

The attraction known as magnetism occurs when a magnetic field is present, which is a field of force produced by a magnetic object or particle. It can also be produced by a changing electric field and is detected by the force it exerts on other magnetic materials. Hence why the area of study dealing with magnets is known as electromagnetism.

Definition:

Magnetic fields can be defined in a number of ways, depending on the context. However, in general terms, it is an invisible field that exerts magnetic force on substances which are sensitive to magnetism. Magnets also exert forces and torques on each other through the magnetic fields they create.

Visualization of the solar wind encountering Earth's magnetic "defenses" known as the magnetosphere. Clouds of southward-pointing plasma are able to peel back layers of the Sun-facing bubble and stack them into layers on the planet's nightside (center, right). The layers can be squeezed tightly enough to reconnect and deliver solar electrons (yellow sparkles) directly into the upper atmosphere to create the aurora. Credit: JPL — *Visualization of the solar wind encountering Earth’s magnetosphere. Like a dipole magnet, it has field lines and a northern and southern pole. Credit: JPL*

They can be generated within the vicinity of a magnet, by an electric current, or a changing electrical field. They are dipolar in nature, which means that they have both a north and south magnetic pole. The Standard International (SI) unit used to measure magnetic fields is the Tesla, while smaller magnetic fields are measured in terms of Gauss (1 Tesla = 10,000 Guass).

Mathematically, a magnetic field is defined in terms of the amount of force it exerted on a moving charge. The measurement of this force is consistent with the Lorentz Force Law, which can be expressed as F= qvB, where F is the magnetic force, q is the charge, v is the velocity, and the magnetic field is B. This relationship is a vector product, where F is perpendicular (->) to all other values.

Field Lines:

Magnetic fields may be represented by continuous lines of force (or magnetic flux) that emerge from north-seeking magnetic poles and enter south-seeking poles. The density of the lines indicate the magnitude of the field, being more concentrated at the poles (where the field is strong) and fanning out and weakening the farther they get from the poles.

A uniform magnetic field is represented by equally-spaced, parallel straight lines. These lines are continuous, forming closed loops that run from north to south, and looping around again. The direction of the magnetic field at any point is parallel to the direction of nearby field lines, and the local density of field lines can be made proportional to its strength.

Magnetic field lines resemble a fluid flow, in that they are streamlined and continuous, and more (or fewer lines) appear depending on how closely a field is observed. Field lines are useful as a representation of magnetic fields, allowing for many laws of magnetism (and electromagnetism) to be simplified and expressed in mathematical terms.

A simple way to observe a magnetic field is to place iron filings around an iron magnet. The arrangements of these filings will then correspond to the field lines, forming streaks that connect at the poles. They also appear during polar auroras, in which visible streaks of light line up with the local direction of the Earth’s magnetic field.

History of Study:

The study of magnetic fields began in 1269 when French scholar Petrus Peregrinus de Maricourt mapped out the magnetic field of a spherical magnet using iron needles. The places where these lines crossed he named “poles” (in reference to Earth’s poles), which he would go on to claim that all magnets possessed.

During the 16th century, English physicist and natural philosopher William Gilbert of Colchester replicated Peregrinus’ experiment. In 1600, he published his findings in a treaties (De Magnete) in which he stated that the Earth is a magnet. His work was intrinsic to establishing magnetism as a science.

View of the eastern sky during the peak of this morning's aurora. Credit: Bob King — *View of the eastern sky during the peak of this morning’s aurora. Credit: Bob King*

In 1750, English clergyman and philosopher John Michell stated that magnetic poles attract and repel each other. The force with which they do this, he observed, is inversely proportional to the square of the distance, otherwise known as the inverse square law.

In 1785, French physicist Charles-Augustin de Coulomb experimentally verified Earths’ magnetic field. This was followed by 19th century French mathematician and geometer Simeon Denis Poisson created the first model of the magnetic field, which he presented in 1824.

By the 19th century, further revelations refined and challenged previously-held notions. For example, in 1819, Danish physicist and chemist Hans Christian Orsted discovered that an electric current creates a magnetic field around it. In 1825, André-Marie Ampère proposed a model of magnetism where this force was due to perpetually flowing loops of current, instead of the dipoles of magnetic charge.

In 1831, English scientist Michael Faraday showed that a changing magnetic field generates an encircling electric field. In effect, he discovered electromagnetic induction, which was characterized by Faraday’s law of induction (aka. Faraday’s Law).

*A Faraday cage in power plant in Heimbach, Germany. Credit: Wikipedia Commons/Frank Vincentz*

Between 1861 and 1865, Scottish scientist James Clerk Maxwell published his theories on electricity and magnetism – known as the Maxwell’s Equations. These equations not only pointed to the interrelationship between electricity and magnetism, but showed how light itself is an electromagnetic wave.

The field of electrodynamics was extended further during the late 19th and 20th centuries. For instance, Albert Einstein (who proposed the Law of Special Relativity in 1905), showed that electric and magnetic fields are part of the same phenomena viewed from different reference frames. The emergence of quantum mechanics also led to the development of quantum electrodynamics (QED).

Examples:

A classic example of a magnetic field is the field created by an iron magnet. As previously mentioned, the magnetic field can be illustrated by surrounding it with iron filings, which will be attracted to its field lines and form in a looping formation around the poles.

Larger examples of magnetic fields include the Earth’s magnetic field, which resembles the field produced by a simple bar magnet. This field is believed to be the result of movement in the Earth’s core, which is divided between a solid inner core and molten outer core which rotates in the opposite direction of Earth. This creates a dynamo effect, which is believed to power Earth’s magnetic field (aka. magnetosphere).

Computer simulation of the Earth's field in a period of normal polarity between reversals.[1] The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of the Earth is centered and vertical. The dense clusters of lines are within the Earth's core — Computer simulation of the Earth’s field in a period of normal polarity between reversals.[1] The lines represent magnetic field lines, blue when the field points towards the center and yellow when away. Credit: NASA

Such a field is called a dipole field because it has two poles – north and south, located at either end of the magnet – where the strength of the field is at its maximum. At the midpoint between the poles the strength is half of its polar value, and extends tens of thousands of kilometers into space, forming the Earth’s magnetosphere.

Other celestial bodies have been shown to have magnetic fields of their own. This includes the gas and ice giants of the Solar System – Jupiter, Saturn, Uranus and Neptune. Jupiter’s magnetic field is 14 times as powerful as that of Earth, making it the strongest magnetic field of any planetary body. Jupiter’s moon Ganymede also has a magnetic field, and is the only moon in the Solar System known to have one.

Mars is believed to have once had a magnetic field similar to Earth’s, which was also the result of a dynamo effect in its interior. However, due to either a massive collision, or rapid cooling in its interior, Mars lost its magnetic field billions of years ago. It is because of this that Mars is believed to have lost most of its atmosphere, and the ability to maintain liquid water on its surface.

When it comes down to it, electromagnetism is a fundamental part of our Universe, right up there with nuclear forces and gravity. Understanding how it works, and where magnetic fields occur, is not only key to understanding how the Universe came to be, but may also help us to find life beyond Earth someday.

We have written many articles about the magnetic field for Universe Today. Here’s What is Earth’s Magnetic Field, Is Earth’s Magnetic Field Ready to Flip?, How Do Magnets Work?, Mapping The Milky Way’s Magnetic Fields – The Faraday Sky, Magnetic Fields in Spiral Galaxies – Explained at Last?, Astronomy Without A Telescope – Cosmic Magnetic Fields.

If you’d like more info on Earth’s magnetic field, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast all about planet Earth. Listen here, Episode 51: Earth.

Sources:

October 21, 2016October 22, 2016 by Matt Williams

MIT Claims they are Programming Humanoid Robots to help Explore Mars. But we all Know It’s Cylons!

NASA's R5 "Valkyrie" robot may become a regular part of future crewed missions to Mars and beyond. Credit: NASA/B. Stafford/J. Blair/R. Geeseman

For over a decade, robots have been exploring Mars in advance of the crewed missions that are being planned for the coming decades. And when it comes time for astronauts to set foot on the Red Planet, they will be looking for robots to help them with some of the legwork. After all, exploring Mars is tough, laborious, and dangerous work, so some robotic assistance will probably be necessary.

For this reason, back in November of 2015, NASA gave the Massachusetts Institute of Technology one of their R5 “Valkyrie” humanoid robots. Since that time, MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) has been developing special algorithms that will allow these robots to help out during future missions to Mars and beyond.

These efforts are being led Professor Russ Tedrake, an electrical engineer and computer programmer who helped program the Atlas robot to take part in the 2015 DARPA Robotics Challenge. Together with members of an advanced independent research group – known as the Super Undergraduate Research Opportunities Program (SuperUROP) – he is getting this R5 robot ready for NASA’s Space Robotics Challenge.

The DARPA Robotics Challenge (DRC) sought to inspire the creation of robots that could perform human tasks, in that case, for the sake of disaster relief. Credit: DARPA — *The DARPA Robotics Challenge (DRC) sought to inspire the creation of robots that could perform human tasks; in that case, for the sake of disaster relief. Credit: DARPA*

As part of NASA’s Centennial Challenges Program, and with a prize purse of $1 million, this competition aims to push the boundaries of what robots are capable of in the realm of space exploration. In addition to MIT, Northeastern University and the University of Edinburgh have been tasked with programming an R5 to complete tasks normally handled by astronauts.

Ultimately, the robots will be tested in a simulated environment and judged based on their ability to complete three tasks. These include aligning a communications array, repairing a broken solar array, and identifying and repairing a habitat leak. There will also be a qualifying round where teams will be tasked with demonstrating autonomous tracking abilities (which will have to be completed in order to move towards the main round).

Naturally, this presents quite a few challenges. NASA designed the R5 robot to be capable of performing human tasks and move like a human being as much as possible, which necessitated a body with 28 torque-controlled joints. However, getting those joints to work together to perform mission-related work and operate independently is a bit of a challenge.

In short, the robot is not like other robotic missions – such as the Opportunity or Curiosity rovers. Instead of having a human being pushing levers to get them to move about and collect samples, the R5 will be tasked with things like opening airlock hatches, attaching and removing power cables, repairing equipment, and retrieving samples all on its own. And of course, if it takes a spill and falls down, it will have to be able to get up on its own.

NASA's Space Robotics Challenge seeks to foster the development of robots that can help human astronauts during future missions, like to Mars. Credit: NASA — *NASA’s Space Robotics Challenge seeks to foster the development of robots that can help human astronauts during future missions, like to Mars. Credit: NASA/STMD*

With the help of the special algorithms being generated by Tedrake and his colleagues – as well as other teams competing in this challenge – robots could play an important role in future missions. This could involve robots selecting landing sites for astronaut crews, setting up habitats in advance of crews arriving, and even conducting preliminary research on celestial bodies.

In addition, robots could take the place of crews on long-distance missions (such as Europa). Instead of sending a crew that would require months of food and supplies, a robot crew could be dispatched to the Jovian moon to collect ice samples, explore the surface, and interface with drones being sent to explore the interior ocean. And if the mission failed, there would be no grieving families (just grieving robotics teams).

And now to address the elephant in the room. The idea of sending robot explorers on space missions to help astronauts (or even replace them) is sure to make some people out there nervous. But for those who fear that this might bring one step closer to a robot revolution, rest assured that the machines are nowhere near where they’d need to be to go all “Judgement Day” on us just yet.

Long before they can launch nuclear weapons, pick up laser guns and stalk us through a post-apocalyptic landscape, or start upgrading themselves to look (and feel) human, robots will first need to master the simple tasks of walking upright and holding a screwdriver.

Still, if any of the robots end up having creepy red visor eyes (or saying things like “by your command”), we might want to consider including the Three Laws of Robotics in their programming. It’s never too soon to make sure they can’t turn on humanity!

Registration for the Space Robotics Challenge opened in August, 2016. The qualifying round, which began in mid-October, will run until mid-December. Finalists of that round will be announced in January, with the final virtual competition taking place in June 2017. The winning team will be awarded $500,000 over a two year period from NASA’s Space Technology Mission Directive.

Further Reading: MIT, NASA

October 21, 2016October 21, 2016 by Bob King

Schiaparelli is Gone. Smashed on the surface of Mars

Mars Reconnaissance Orbiter view of Schiaparelli landing site before and after the lander arrived. The images have a resolution of 6 meters per pixel and shows two new features on the surface when compared to an image from the same camera taken in May this year. The black dot appears to be the lander impact site and the smaller white dot below the paw-shaped cluster of craters, the parachute. Credit: NASA

Instead of a controlled descent to the surface using its thrusters, ESA’s Schiaparelli lander hit the ground hard and may very well have exploded on impact. NASA’s Mars Reconnaissance Orbiter then-and-now photos of the landing site have identified new markings on the surface of the Red Planet that are believed connected to the ill-fated lander.

Schiaparelli entered the martian atmosphere at 10:42 a.m. EDT (14:42 GMT) on October 19 and began a 6-minute descent to the surface, but contact was lost shortly before expected touchdown seconds after the parachute and back cover were discarded. One day later, the Mars Reconnaissance Orbiter took photos of the expected touchdown site as part of a planned imaging run.

The landing site is shown within the Schiaparelli landing ellipse (top) along with before and after images below. Copyright Main image: NASA/JPL-Caltech/MSSS, Arizona State University; inserts: NASA/JPL-Caltech/MSSS

One of the features is bright and can be associated with the 39-foot-wide (12-meter) diameter parachute used in the second stage of Schiaparelli’s descent. The parachute and the associated back shield were released from Schiaparelli prior to the final phase, during which its nine thrusters should have slowed it to a standstill just above the surface.

The other new feature is a fuzzy dark patch or crater roughly 50 x 130 feet (15 x 40 meters) across and about 0.6 miles (1 km) north of the parachute. It’s believed to be the impact crater created by the Schiaparelli module following a much longer free fall than planned after the thrusters were switched off prematurely.

Artist's concept of Schiaparelli deploying its parachute. The parachute may also have played a role in the crash. It may have deployed too soon, causing the thrusters to fire up too soon and run out of fuel. Or the thrusters may have simply cut out after firing. Credit: ESA — Artist’s concept of Schiaparelli deploying its parachute. The parachute may also have played a role in the crash. It may have deployed too soon, causing the thrusters to fire too soon. The thrusters may also have simply cut out too soon after firing. Credit: ESA

Mission control estimates that Schiaparelli dropped from between 1.2 and 2.5 miles (2 and 4 km) altitude, striking the Martian surface at more than 186 miles an hour (300 km/h). The dark spot is either disturbed surface material or it could also be due to the lander exploding on impact, since its thruster propellant tanks were likely still full. ESA cautions that these findings are still preliminary.

Something went wrong with Schiaparelli's one or more sets of thrusters during the descent. Credit: ESA — Something went wrong with Schiaparelli’s one or more sets of thrusters during the descent, causing the lander to crash on the surface at high speed. Credit: ESA

Since the module’s descent trajectory was observed from three different locations, the teams are confident that they will be able to reconstruct the chain of events with great accuracy. Exactly what happened to cause the thrusters to shut down prematurely isn’t yet known.

October 21, 2016 by Bob King

Astronomers Think They Know Where Rosetta’s Comet Came From

In the distant past, the orbit of 67P/Churyumov-Gerasimenko extended far beyond Neptune into the refrigerated Kuiper Belt. Interactions with the gravitational giant Jupiter altered the comet's orbit over time, dragging it into the inner Solar System. Credit: Western University, Canada

Rosetta’s Comet hails from a cold, dark place. Using statistical analysis and scientific computing, astronomers at Western University in Canada have charted a path that most likely pinpoints comet 67P/Churyumov-Gerasimenko’s long-ago home in the far reaches of the Kuiper Belt, a vast region beyond Neptune home to icy asteroids and comets.

According to the new research, Rosetta’s Comet is relative newcomer to the inner parts of our Solar System, having only arrived about 10,000 years ago. Prior to that, it spent the last 4.5 billion years in cold storage in a rough-and-tumble region of the Kuiper Belt called the scattered disk.

The Kuiper Belt was named in honor of Dutch-American astronomer Gerard Kuiper, who postulated a reservoir of icy bodies beyond Neptune. The first Kuiper Belt object was discovered in 1992. We now know of more than a thousand objects there, and it's estimated it's home to more than 100,000 asteroids and comets there over 62 miles (100 km) across. Credit: JHUAPL — The Kuiper Belt was named in honor of Dutch-American astronomer Gerard Kuiper, who postulated a reservoir of icy bodies beyond Neptune. The first Kuiper Belt object was discovered in 1992. We now know of more than a thousand objects there, and it’s estimated it’s home to more than 100,000 asteroids and comets there over 62 miles (100 km) across. Credit: JHUAPL

In the Solar System’s youth, asteroids that strayed too close to Neptune were scattered by the encounter into the wild blue yonder of the disk. Their orbits still bear the scars of those long-ago encounters: they’re often highly-elongated (shaped like a cigar) and tilted willy-nilly from the ecliptic plane up to 40°. Because their orbits can take them hundreds of Earth-Sun distances into the deeps of space, scattered disk objects are among the coldest places in the Solar System with surface temperatures around 50° above absolute zero. Ices that glommed together to form 67P at its birth are little changed today. Primordial stuff.

Watch how Rosetta’s Comet’s orbit has evolved since the comet’s formation

There are two basic comet groups. Most comets reside in the cavernous Oort Cloud, a roughly spherical-shaped region of space between 10,000 and 100,000 AU (astronomical unit = one Earth-Sun distance) from the Sun. The other major group, the Jupiter-family comets, owes its allegiance to the powerful gravity of the giant planet Jupiter. These comets race around the Sun with periods of less than 20 years. It’s thought they originate from collisions betwixt rocky-icy asteroids in the Kuiper Belt.

Fragments flung from the collisions are perturbed by Neptune into long, cigar-shaped orbits that bring them near Jupiter, which ropes them like calves with its insatiable gravity and re-settles them into short-period orbits.

Comet 67P/Churyumov-Gerasimenko is a Jupiter-family comet. Its 6.5 year journey around the Sun takes it from just beyond the orbit of Jupiter at its most distant, to between the orbits of Earth and Mars at its closest. Credit: ESA with labels by the author — Comet 67P/Churyumov-Gerasimenko is a Jupiter-family comet. Its 6.5 year journey around the Sun takes it from just beyond the orbit of Jupiter at its most distant to between the orbits of Earth and Mars at its closest. Credit: ESA with labels by the author

Mattia Galiazzo and solar system expert Paul Wiegert, both at Western University, showed that in transit, Rosetta’s Comet likely spent millions of years in the scattered disk at about twice the distance of Neptune. The fact that it’s now a Jupiter family comet hints of a possible long-ago collision followed by gravitational interactions with Neptune and Jupiter before finally becoming an inner Solar System homebody going around the Sun every 6.45 years.

By such long paths do we arrive at our present circumstances.

October 21, 2016March 27, 2017 by Fraser Cain

Weekly Space Hangout – October 21, 2016: Dr. Voula Saridakis of @histastro & Morgan is a Tilted Sun

Host: Fraser Cain (@fcain)

Special Guest:
This week’s special guest is Dr. Voula Saridakis, a professor at Lake Forest College in Illinois specializing in the history of science and astronomy, who runsthe History of Astronomy on Twitter at @histastro

Guests:
Morgan Rehnberg (MorganRehnberg.com / @MorganRehnberg)
Kimberly Cartier ( KimberlyCartier.org / @AstroKimCartier )
Alessondra Springmann (sondy.com / @sondy)
Nicole Gugliucci (cosmoquest.org / @noisyastronomer)

Their stories this week:

Schiaparelli /TGO
The Unexpected Detection of Dark Matter Galaxies
News from DPS:
Planet 9
Juno
Exomars
Comet 67p

We use a tool called Trello to submit and vote on stories we would like to see covered each week, and then Fraser will be selecting the stories from there. Here is the link to the Trello WSH page (http://bit.ly/WSHVote), which you can see without logging in. If you’d like to vote, just create a login and help us decide what to cover!

If you would like to join the Weekly Space Hangout Crew, visit their site here and sign up. They’re a great team who can help you join our online discussions!

If you would like to sign up for the AstronomyCast Solar Eclipse Escape, where you can meet Fraser and Pamela, plus WSH Crew and other fans, visit our site linked above and sign up!

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Universe Today, or the Universe Today YouTube page.

October 20, 2016October 20, 2016 by Matt Williams

Mars’ Moon Deimos

The Moons of Mars — Image of the Martian Moon of Deimos, as imaged by the Mars Reconnaissance Orbiter. Credit: HiRISE/MRO/LPL (U. Arizona)/NASA

Mars and Earth have several things in common. Like Earth, Mars is a terrestrial planet (i.e. composed of silicate rock and minerals). It also has polar ice caps, a tilted axis, and evidence of liquid water on its surface. On top of that, Mars and Earth are the only terrestrial planets in the Solar System to have natural satellites.

In fact, Mars has two satellites, which are appropriately named Phobos and Deimos (named after the Greek gods of horror and terror, respectively). Of the two, Deimos is the smaller moon and orbits at a greater distance from the planet. And like Deimos, it has the characteristics of an asteroid, which is a strong indication of where it may have come from.

Discovery and Naming:

Deimos was discovered in 1877 by American astronomer Asaph Hall, who was deliberately searching for Martian moons at the United States Naval Observatory (USNO). Its name was suggested shortly thereafter by Henry Madan, the Science Master of Eton College, and was derived from Homer’s The Iliad.

Phobos and Deimos, photographed here by the Mars Reconnaissance Orbiter, are tiny, irregularly-shaped moons that are probably strays from the main asteroid belt. Credit: NASA - See more at: http://astrobob.areavoices.com/2013/07/05/rovers-capture-loony-moons-and-blue-sunsets-on-mars/#sthash.eMDpTVPT.dpuf — *Phobos and Deimos, photographed by the Mars Reconnaissance Orbiter. Credit: NASA/JPL*

Size, Mass and Orbit:

Deimos has a mean radius of between 6 and 6.38 km (3.73 – 3.96 mi). However, the moon is not a round body, and measures roughly 15 × 12.2 × 11 km (9.32 x 7.58 x 6.835 mi), making it 0.56 times the size of Phobos. At 1.4762 × 10¹⁵ kg, or 1.4762 trillion metric tons, Deimos is 1/49,735,808 times as massive as the Moon. As a result, Deimos’ surface gravity is very weak, just 0.003 m/s – or 0.000306 g.

Deimos’ orbit is nearly circular, ranging from 23455.5 km at periapsis (closest) to 23470.9 km at apoapsis (farthest) – which works out to an average distance (semi-major axis) of 23,463.2 km. With an average orbital speed of 1.3513 km/s, it takes 30 hours, 18 minutes and 43.2 seconds to complete a single orbit (or 1.263 days).

Composition and Surface Features:

Deimos, like Phobos, is similar in composition to carbonaceous chondrite and silicate/carbon-rich (C- and D-type) asteroids. Though the surface is cratered, it is considerably smoother than Phobos’ surface, which is due to its craters being filled with regolith.

Only two geological features on Deimos have been given names – the craters of Voltaire and Swift. These features take their names from the famous 17th/18th century French and English writers who speculated about the existence of two Martian moons before they were even discovered.

HiRISE captured these enhanced-color images of Deimos, the smaller of the two moons of Mars, on 21 February 2009. Credit: NASA/JPL — *Image of Deimos captured by HiRISE, showing the craters of Voltaire and Swift in the upper left corner. Credit: NASA/JPL/University of Arizona*

Origin:

The origin of Mars’ moons remains unknown, but some hypotheses exist. The most widely-accepted theory states that, based on their similarity to C- or D-type asteroids, they are objects that were kicked out of the Asteroid Belt by Jupiter’s gravity. They were then captured by Mars’ and fell into their current orbits due to atmospheric drag or tidal forces.

However, this theory remains controversial since Mars’ current atmosphere is too thin. As such, it is highly unlikely that it would have been able to cause enough drag to slow either moon down enough for them to have achieved their current orbits. A modified version of this hypothesis is that Phobos and Deimos were once a binary asteroid, which was then captured and separated by tidal forces.

Other popular hypotheses include that they were formed by accretion in their current orbits, or that Mars was once surrounded by many large asteroids which were ejected into orbit it after a collision with a planetesimal – like the one that formed Earth’s Moon. Over time, these would have fallen back to the surface until only Phobos and Deimos remained.

Exploration:

Overall, Deimos history of exploration is tied to that of Mars and Phobos. While no landings have been made on its surface, several have been proposed in the past. The first of these were made as part of the Soviet Phobos (Fobos) program, which involved two probes – Fobos 1 and 2 – that were launched in July of 1988.

If the first proved successful in landing on Phobos, the second would been diverted to make a landing on Deimos. However, the first probe was lost en route to Mars while the second managed to returned some data and images of Phobos surface before contact was lost.

In 1997-1998, NASA selected the proposed Aladdin mission as a finalist for its Discovery Program. The plan was to visit both Phobos and Deimos with sample return missions involving an orbiter and lander. After reaching the surface, the landers would collect samples and then launch them back to the orbiters (which would return them to Earth). However, the mission was passed over in favor of the MESSENGER probe, which was sent to study Mercury.

Other missions have been proposed with are still under study. These include the “Hall” concept proposed in 2008, which calls for a probe that relies on solar-electric propulsion (SEP) to reach Mars and return with samples to Earth. Another was the Gulliver mission, a concept proposed in 2010 which would attempt to retrieve 1 kg (2.2 lbs) of material from Deimos’ surface.

The planners behind the OSIRIS-REx mission have also proposed mounting a second mission that would return samples from Phobos and Deimos. And at the 2014 Lunar and Planetary Science Conference, a proposal was made for a low-cost mission based on the Lunar Atmosphere Dust and Environment Explorer. It is named the Phobos and Deimos & Mars Environment (PADME) mission, and would involve an orbiter being sent to Mars by 2021.

Deimos has been photographed from the surface of Mars by both the Opportunity and Curiosity rovers. And someday, actual astronauts may be able to look up at it from the Martian surface. From their point of view, Deimos would appear like a star to the unaided eye. At its brightest, it might look like Venus does from here on Earth.

For those watching over an extended period of time, Deimos would pass directly in front of the Sun quite regularly. It’s too small to cause a total eclipse, it would look like a black dot moving across the face of the Sun.

We have written many interesting articles about Mars’ moons here at Universe Today. Here’s How Many Moons Does Mars Have?, Phobos and Deimos – the Moons of Mars Explained, Phobos and Deimos Together at Last!, Moon Dance: Curiosity Rover Captures Movie of Phobos and Deimos Together and Opportunity sees Phobos and Deimos.

For more information, be sure to check out this Solar Views article on Deimos.

Astronomy Cast also has some relevant episodes on the subject – Episode 52: Mars, and Episode 91: The Search for Water on Mars.

Sources:

October 20, 2016 by Evan Gough

No, There Won’t Be 15 Days of Darkness in November. It’s Another Stupid Hoax.

Venus and Jupiter at dusk over Australia's Outback on June 27, 2015. Credit: Joseph Brimacombe

The internet is great, isn’t it?

You can post anything you want on the internet, and if people like the sound of it, they spread it. It doesn’t make any difference if it’s true or not. We’re not born fact checkers and skeptics, are we?

Pretty soon, before you know it, it’s gone viral. Then it becomes its own sensation, and people who don’t even believe it start reporting it. Never is this more true than with hoaxes.

The latest hoax is the “15 Days of Darkness in November” thing that’s going around. Everyone’s on the bandwagon.

The 15 days hoax is not new. It made an appearance last year, and was thoroughly debunked. And of course, there wasn’t 15 day of darkness last year, was there? (Unless NASA covered it up!)

It’s here again this year, and will be debunked again, and will probably be here next year, too.

The whole thing started at a site that will remain linkless, and caught on from there. This is what the site reported:

“NASA has confirmed that the Earth will experience 15 days of total darkness between November 15 and November 29, 2015. The event, according to NASA, hasn’t occurred in over 1 Million years.”

Of course, NASA never said any such thing.

Here is supposedly what will happen to cause this calamity. Try and follow along with the nonsensical foolishness.

During the conjunction between Venus and Jupiter on October 26, light from Venus would cause gases in Jupiter to heat up. The heated gasses will cause a large amount of hydrogen to be released into space. The gases will reach the Sun and trigger a massive explosion on the surface of the star, heating it to 9,000 degrees Kelvin. The heat of the explosion would then cause the Sun to emit a blue color.
The dull blue color will last for 15 days during which the Earth will be thrown into darkness.

Where to begin? Let’s start with conjunctions.

Conjunctions are mostly just visual phenomena. The fact that two things in the sky look closer together from our point of view on Earth doesn’t mean that they’re that close together. In fact, even when Jupiter and Venus are in conjunction, they can still be over 800 million km apart. For perspective, the Sun and the Earth are about 150 million km apart.

So, as the hoax goes, at that great distance, light from Venus will cause gases on Jupiter to heat up. News Flash: the light from the Sun is far more intense than light from Venus could ever be, and it doesn’t heat up the gases on Jupiter. In fact, any light from Venus that makes it to Jupiter is just reflected sunlight anyway.

The Moon and this dead tree are in conjunction. This will cause the Martian Pyramids to vibrate harmonically. These vibrations will shake the walls of the movie studio where the Moon landing was faked, causing it to collapse. Image: Evan Gough

The hoax gets more outrageous as it goes along. These supposed heated gases then escape from Jupiter into space, and head for the Sun. But Jupiter is enormous and has enormous gravitational pull. How are any gases going to escape Jupiter’s overpowering gravity? Answer: they can’t and they won’t.

Then, these gases supposedly strike the Sun, and trigger a massive explosion on the Sun’s surface, which turn the Sun blue and plunges the Earth into darkness. Not blueness, which I could understand, but darkness.

This is absurd, of course. The Sun dominates the planets in a one-way relationship, and nothing the planets ever do could change that. No escaped gases from Jupiter would ever strike the Sun.

Jupiter is puny and insignificant compared to the Sun. And it's also hundreds of millions of kilometers away. How is a puny puff of hydrogen from Jupiter supposed to darken the Sun? Image: NASA/SDO — Jupiter is puny and insignificant compared to the Sun. And it’s also hundreds of millions of kilometers away. How is a puny puff of hydrogen from Jupiter supposed to darken the Sun? Image: NASA/SDO

Nothing Jupiter does can affect the Sun. Jupiter is, on average, 778 million km from the Sun. Jupiter could change places with Venus, and the Sun would keep shining normally. Jupiter could explode completely and the Sun would go on shining normally. Jupiter could put on a big red nose and some clown shoes, and the Sun would remain unaffected.

The Sun is a giant atom-crushing machine 1000 times more massive than Jupiter. The massive wall of energy and solar wind that comes from the Sun slams into Jupiter, and completely overwhelms anything Jupiter can do to the Sun. It’s just the way it is. It’s just the way it will always be.

Like the faked Moon landing hoax, and the Nibiru/Planet X hoax, this 15 days of darkness meme just keeps coming around. There may be no end to it.

It’s annoying, for sure, but maybe there’s a silver lining. Maybe some people reading about this supposed calamity will enter the word “conjunction” into a search engine, and begin their own personal journey of learning how the universe works.

We can hope so, can’t we?

October 20, 2016 by Susie Murph

Carnival of Space #479

Carnival of Space. Image by Jason Major.

This week’s Carnival of Space is hosted by Allen Versfeld at his Urban Astronomer blog.

Click here to read Carnival of Space #479.
Continue reading “Carnival of Space #479”

October 20, 2016 by Fraser Cain

What is a Nova?

There are times when I really wish astronomers could take their advanced modern knowledge of the cosmos and then go back and rewrite all the terminology so that they make more sense. For example, dark matter and dark energy seem like they’re linked, and maybe they are, but really, they’re just mysteries.

Is dark matter actually matter, or just a different way that gravity works over long distances? Is dark energy really energy, or is it part of the expansion of space itself. Black holes are neither black, nor holes, but that doesn’t stop people from imagining them as dark tunnels to another Universe. Or the Big Bang, which makes you think of an explosion.

Another category that could really use a re-organizing is the term nova, and all the related objects that share that term: nova, supernova, hypernova, meganova, ultranova. Okay, I made those last couple up.

I guess if you go back to the basics, a nova is a star that momentarily brightens up. And a supernova is a star that momentarily brightens up… to death. But the underlying scenario is totally different.

New research shows that some old stars known as white dwarfs might be held up by their rapid spins, and when they slow down, they explode as Type Ia supernovae. Thousands of these "time bombs" could be scattered throughout our Galaxy. In this artist's conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet. Credit: David A. Aguilar (CfA) — In this artist’s conception, a supernova explosion is about to obliterate an orbiting Saturn-like planet. Credit: David A. Aguilar (CfA)

As we’ve mentioned in many articles already, a supernova commonly occurs when a massive star runs out of fuel in its core, implodes, and then detonates with an enormous explosion. There’s another kind of supernova, but we’ll get to that later.

A plain old regular nova, on the other hand, happens when a white dwarf – the dead remnant of a Sun-like star – absorbs a little too much material from a binary companion. This borrowed hydrogen undergoes fusion, which causes it to brighten up significantly, pumping up to 100,000 times more energy off into space.

Imagine a situation where you’ve got two main sequence stars like our Sun orbiting one another in a tight binary system. Over the course of billions of years, one of the stars runs out of fuel in its core, expands as a red giant, and then contracts back down into a white dwarf. It’s dead.

Some time later, the second star dies, and it expands as a red giant. So now you’ve got a red dwarf and a white dwarf in this binary system, orbiting around and around each other, and material is streaming off the red giant and onto the smaller white dwarf.

Illustration of a white dwarf feeding off its companion star Credit: ESO / M. Kornmesser

This material piles up on the surface of the white dwarf forming a cosy blanket of stolen hydrogen. When the surface temperature reaches 20 million kelvin, the hydrogen begins to fuse, as if it was the core of a star. Metaphorically speaking, its skin catches fire. No, wait, even better. Its skin catches fire and then blasts off into space.

Over the course of a few months, the star brightens significantly in the sky. Sometimes a star that required a telescope before suddenly becomes visible with the unaided eye. And then it slowly fades again, back to its original brightness.

Some stars do this on a regular basis, brightening a few times a century. Others must clearly be on a longer cycle, we’ve only seen them do it once.

Astronomers think there are about 40 novae a year across the Milky Way, and we often see them in other galaxies.

The term “nova” was first coined by the Danish astronomer Tycho Brahe in 1572, when he observed a supernova with his telescope. He called it the “nova stella”, or new star, and the name stuck. Other astronomers used the term to describe any star that brightened up in the sky, before they even really understood the causes.

During a nova event, only about 5% of the material gathered on the white dwarf is actually consumed in the flash of fusion. Some is blasted off into space, and some of the byproducts of fusion pile up on its surface.

Tycho's Supernova Remnant. Credit: Spitzer, Chandra and Calar Alto Telescopes. — Tycho’s Supernova Remnant. Credit: Spitzer, Chandra and Calar Alto Telescopes.

Over millions of years, the white dwarf can collect enough material that carbon fusion can occur. At 1.4 times the mass of the Sun, a runaway fusion reaction overtakes the entire white dwarf star, releasing enough energy to detonate it in a matter of seconds.

If a regular nova is a quick flare-up of fusion on the surface of a white dwarf star, then this event is a super nova, where the entire star explodes from a runaway fusion reaction.

You might have guessed, this is known as a Type 1a supernova, and astronomers use these explosions as a way to measure distance in the Universe, because they always explode with the same amount of energy.

Hmm, I guess the terminology isn’t so bad after all: nova is a flare up, and a supernova is a catastrophic flare up to death… that works.

Now you know. A nova occurs when a dead star steals material from a binary companion, and undergoes a momentary return to the good old days of fusion. A Type Ia supernova is that final explosion when a white dwarf has gathered its last meal.

October 20, 2016October 20, 2016 by Nancy Atkinson

Here Are the Last Images We’ll Ever See From Rosetta

The last set of images taken by the Rosetta spacecraft's NAVCAM during the final month of its mission. ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.

The Rosetta team has released the final batch of images taken by the NAVCAM during the last month of its two years of investigations at Comet 67P/Churyumov-Gerasimenko. It’s a big batch and they are absolutely stunning, but its sad to know they are the last NAVCAM images. The image set covers the period from September 2-30, 2016 when the spacecraft was on elliptical orbits that sometimes brought it to within 2 km of the comet’s surface, so you’ll see a wide variety of imagery with a variety of geology and lighting conditions.

Take a look below:

A large boulder sits precariously on Comet 67P/Churyumov-Gerasimenko as seem by Rosetta's NAVCAM on September 11, 2016. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0. — A large boulder sits precariously on Comet 67P/Churyumov-Gerasimenko as seem by Rosetta’s NAVCAM on September 11, 2016. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.

While these are the final NAVCAM images, there may be more images coming from the OSIRIS camera. Also, many other instruments will be releasing data, as they were active as long as possible before impact. Many of the science instruments were expected to return their last data from between 20 meters to 5 meters above the surface.

ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) collected data on the density of gas around the comet and its composition while GIADA (Grain Impact Analyser and Dust Accumulator) measured the dust density.

RPC’s (Rosetta Plasma Consortium) instrument suite provided a look at interaction between the solar wind and the surface of the comet. Alice, an Ultraviolet Imaging Spectrometer similar to the one on New Horizons, took high resolution ultraviolet spectra of the surface. RSI (Radio Science Investigation) got the most accurate measurements of the gravity field during descent.

A variety of geology and light on on Comet 67P/Churyumov-Gerasimenko as seem by Rosetta's NAVCAM on September 5, 2016. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0. — A variety of geology and light on on Comet 67P/Churyumov-Gerasimenko as seem by Rosetta’s NAVCAM on September 5, 2016. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.

A field of bright bolders on Comet 67P/Churyumov-Gerasimenko as seem by Rosetta's NAVCAM during September 2-20. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0. — A field of bright bolders on Comet 67P/Churyumov-Gerasimenko as seem by Rosetta’s NAVCAM during September 2-20. Credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.

And here’s one of the last five images from Rosetta’s NAVCAM as it descended to its controlled impact on September 30 onto Comet 67P, taking incredible, close-up images during descent, this one just 18.1 km up. It shows the “drippy icing” landscape on this portion of the comet:

Single frame enhanced NavCam image taken on September 30, 2016 at 00:27 GMT, when Rosetta was 18.1 km from the center of the nucleus of Comet 67P/Churyumov-Gerasimenko. The scale at the surface is about 1.5 m/pixel and the image measures about 1.6 km across. ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0.

You can see all the final images at the Rosetta blog.