Posted on by Matt Williams

Where is Earth in the Milky Way?

Artist's impression of The Milky Way Galaxy. Based on current estimates and exoplanet data, it is believed that there could be tens of billions of habitable planets out there. Credit: NASA

For thousand of years, astronomers and astrologers believed that the Earth was at the center of our Universe. This perception was due in part to the fact that Earth-based observations were complicated by the fact that the Earth is embedded in the Solar System. It was only after many centuries of continued observation and calculations that we discovered that the Earth (and all other bodies in the Solar System) actually orbits the Sun.

Much the same is true about our Solar System’s position within the Milky Way. In truth, we’ve only been aware of the fact that we are part of a much larger disk of stars that orbits a common center for about a century. And given that we are embedded within it, it has been historically difficult to ascertain our exact position. But thanks to ongoing efforts, astronomers now know where our Sun resides in the galaxy.

Size of the Milky Way:

For starters, the Milky Way is really, really big! Not only does it measure some 100,000–120,000 light-years in diameter and about 1,000 light-years thick, but up to 400 billion stars are located within it (though some estimates think there are even more). Since one light year is about 9.5 x 1012 km (9.5 trillion km) long, the diameter of the Milky Way galaxy is about 9.5 x 1017 to 11.4 x 1017 km, or 9,500 to 11,400 quadrillion km.

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.

And yet, our galaxy is only a middle-weight when compared to other galaxies in the local Universe. Andromeda, the closest major galaxy to our own, is about twice as large as our own. It measures 220,000 light years in diameter, and has an estimated 400-800 billion stars within it.

Structure of the Milky Way:

If you could travel outside the galaxy and look down on it from above, you’d see that the Milky Way is a barred spiral galaxy. For the longest time, the Milky Way was thought to have 4 spiral arms, but newer surveys have determined that it actually seems to just have two spiral arms, called Scutum–Centaurus and Carina–Sagittarius.

The spiral arms are formed from density waves that orbit around the Milky Way – i.e. stars and clouds of gas clustered together. As these density waves move through an area, they compress the gas and dust, leading to a period of active star formation for the region. However, the existence of these arms has been determined from observing parts of the Milky Way – as well as other galaxies in our universe.

The Milky Way's basic structure is believed to involve two main spiral arms emanating from opposite ends of an elongated central bar. But only parts of the arms can be seen - gray segments indicate portions not yet detected. Other known spiral arm segments--including the Sun's own spur--are omitted for clarity. Credit: T. Dame
The Milky Way’s basic structure is believed to involve two main spiral arms emanating from opposite ends of an elongated central bar. Credit: T. Dame

In truth, all the pictures that depict our galaxy are either artist’s renditions or pictures of other spiral galaxies, and not the result of direct observation of the whole. Until recently, it was very difficult for scientists to gauge what the Milky Way really looks like, mainly because we’re inside it. It has only been through decades of observation, reconstruction and comparison to other galaxies that they have been to get a clear picture of what the Milky Way looks like from the outside.

From ongoing surveys of the night sky with ground-based telescopes, and more recent missions involving space telescopes, astronomers now estimate that there are between 100 and 400 billion stars in the Milky Way. They also think that each star has at least one planet, which means there are likely to be hundreds of billions of planets in the Milky Way – billions of which are believed to be the size and mass of the Earth.

As noted, much of the Milky Way’s arms is made up of dust and gas. This matter makes up a whopping 10-15% of all the “luminous matter” (i.e. that which is visible) 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. What’s more, infrared astronomy and viewing the Universe in other, non-visible wavelengths has allowed astronomers to be able to see more of it.

The Milky Way, like all galaxies, is also surrounded by a vast halo of dark matter, which accounts for some 90% of its mass. Nobody knows precisely what dark matter is, but its mass has been inferred by observations of how fast the galaxy rotates and other general behaviors. More importantly, it is believed that this mass helps keep the galaxy from tearing itself apart as it rotates.

The Solar System:

The Solar System (and Earth) is located about 25,000 light-years to the galactic center and 25,000 light-years away from the rim. So basically, if you were to think of the Milky Way as a big record, we would be the spot that’s roughly halfway between the center and the edge.

Astronomers have agreed that the Milky Way probably has two major spiral arms – Perseus arm and the Scutum-Centaurus arm – with several smaller arms and spurs. The Solar System is located in a region in between the two arms called the Orion-Cygnus arm. This arm measures 3,500 light-years across and is 10,000 light-years in length, where it breaks off from the Sagittarius Arm.

our location in the Orion Spur of the Milky Way galaxy. image credit: Roberto Mura/Public Domain
The location of our Solar Systemin the Orion Spur of the Milky Way galaxy. Credit: Roberto Mura/Public Domain

The fact that the Milky Way divides the night sky into two roughly equal hemispheres indicates that the Solar System lies near the galactic plane. The Milky Way has a relatively low surface brightness due to the gases and dust that fills the galactic disk. That prevents us from seeing the bright galactic center or from observing clearly what is on the other side of it.

You might be surprised to learn that it takes the Sun 250 million years to complete one rotation around the Milky Way – this is what is known as a “Galactic Year” or “Cosmic Year”. The last time the Solar System was in this position in the Milky Way, there were still dinosaurs on Earth. The next time, who knows? Humanity might be extinct, or it might have evolved into something else entirely.

As you can see, the Milky Way alone is a very big place. And discerning our location within it has been no simple task. And as our knowledge of the Universe has expanded, we’ve come to learn two things. Not only is the Universe much larger than we could have ever imagined, but our place within in continues to shrink! Our Solar System, it seems, is both insignificant in the grand scheme of things, but also extremely precious!

We have written many 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?

If you’d like more info on the Milky Way, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.

We’ve also recorded an episode of Astronomy Cast all about the Milky Way. Listen here, Episode 99: The Milky Way.

Posted on by Evan Gough

New Dwarf Planet Discovered Beyond Neptune

2015 RR245's orbit takes it 120 times further from the Sun than the Earth is. Image: OSSOS/Alex Parker
2015 RR245's orbit takes it 120 times further from the Sun than the Earth is. Image: OSSOS/Alex Parker

A new dwarf planet has been discovered beyond Neptune, in the disk of small icy worlds that resides there. The planet was discovered by an international team of astronomers as part of the Outer Solar Systems Origins Survey (OSSOS). The instrument that found it was the Canada-France Hawaii Telescope at Maunakea, Hawaii.

The planet is about 700 km in size, and has been given the name 2015 RR245. It was first sighted by Dr. JJ Kavelaars, of the National Research Council of Canada, in images taken in 2015. Dwarf planets are notoriously difficult to spot, but they’re important pieces of the puzzle in tracing the evolution of our Solar System.

Dr. Michele Bannister, of the University of Victoria in British Columbia, describes the moment when the planet was discovered: “There it was on the screen— this dot of light moving so slowly that it had to be at least twice as far as Neptune from the Sun.”

These images show 3 hours of RR245's movement. Image: OSSOS
These images show 3 hours of RR245’s movement. Image: OSSOS

“The icy worlds beyond Neptune trace how the giant planets formed and then moved out from the Sun. They let us piece together the history of our Solar System. But almost all of these icy worlds are painfully small and faint: it’s really exciting to find one that’s large and bright enough that we can study it in detail.” said Bannister.

As the New Horizons mission has shown us, these far-flung, cold bodies can have exotic features in their geological landscapes. Where once Pluto, king of the dwarf planets, was thought to be a frozen body locked in time, New Horizons revealed it to be a much more dynamic place. The same may be true of RR245, but for now, not much is known about it.

The 700 km size number is really just a guess at this point. More measurements will need to be taken of its surface properties to verify its size. “It’s either small and shiny, or large and dull.” said Bannister.

As our Solar System evolved, most dwarf planets like RR245 were destroyed in collisions, or else flung out into deep space by gravitational interactions as the gas giants migrated to their current positions. RR245 is one of the few that have survived. It now spends its time the same way other dwarf planets like Pluto and Eris do, among the tens of thousands of small bodies that orbit the sun beyond Neptune.

RR245 has not been observed for long, so much of what’s known about its orbit will be refined by further observation. But at this point it appears to have a 700 year orbit around the Sun. And it looks like for at least the last 100 million years it has travelled its current, highly elliptical orbit. For hundreds of years, it has been further than 12 billion km (80 AU)from the Sun, but by 2096 it should come within 5 billion km (34 AU) of the Sun.

The discovery of RR 245 came as a bit of a surprise to the OSSOS team, as that’s not their primary role. “OSSOS was designed to map the orbital structure of the outer Solar System to decipher its history,” said Prof. Brett Gladman of the University of British Columbia in Vancouver. “While not designed to efficiently detect dwarf planets, we’re delighted to have found one on such an interesting orbit”.

OSSOS has discovered over 500 hundred trans-Neptunian objects, but this is the first dwarf planet it’s found. “OSSOS is only possible due to the exceptional observing capabilities of the Canada-France-Hawaii Telescope. CFHT is located at one of the best optical observing locations on Earth, is equipped with an enormous wide-field imager, and can quickly adapt its observing each night to new discoveries we make. This facility is truly world leading.” said Gladman.

If RR 245's diameter is conclusively measured as 700 km, it will be smaller than the dwarf planet Ceres, which is 945 km in diameter. Image courtesy of NASA.
If RR 245’s diameter is conclusively measured as 700 km, it will be smaller than the dwarf planet Ceres, which is 945 km in diameter. Image courtesy of NASA.

A lot of work has been done to find dwarf planets in the far reaches of our Solar System. It may be that RR 245 is the last one we find. If there are any more out there, they may have to wait until larger and more powerful telescopes become available. In the mid-2020’s, the Large Synoptic Survey Telescope (LSST) will come on-line in Chile. That ‘scope features a 3200 megapixel camera, and each image it captures will be the size of 40 full Moons. It’ll be hard for any remaining dwarf planets to hide from that kind of imaging power.

As for RR 245’s rather uninspiring name, it will have to do for a while. But as the discoverers of the new dwarf planet, the OSSOS team will get to submit their preferred name for the planet. After that, it’s up the International Astronomical Union (IAU) to settle on one.

What do you think? If this is indeed the last dwarf planet to be found in our Solar System what should we call it?

Posted on by Matt Williams

What are the Jovian Planets?

The Jovian planets of the Solar System. Credit: bork.hampshire.edu

Beyond our Solar System’s “Frost Line” – the region where volatiles like water, ammonia and methane begin to freeze – four massive planets reside. Though these planets – Jupiter, Saturn, Uranus and Neptune – vary in terms of size, mass, and composition, they all share certain characteristics that cause them to differ greatly from the terrestrial planets located in the inner Solar System.

Officially designated as gas (and/or ice) giants, these worlds also go by the name of “Jovian planets”. Used interchangeably with terms like gas giant and giant planet, the name describes worlds that are essentially “Jupiter-like”. And while the Solar System contains four such planets, extra-solar surveys have discovered hundreds of Jovian planets, and that’s just so far…

Definition:

The term Jovian is derived from Jupiter, the largest of the Outer Planets and the first to be observed using a telescope  – by Galileo Galilei in 1610. Taking its name from the Roman king of the gods – Jupiter, or Jove – the adjective Jovian has come to mean anything associated with Jupiter; and by extension, a Jupiter-like planet.

The giant planets of the Solar System (aka. Jovians). Credit: spiff.rit.edu
The giant planets of the Solar System (aka. the Jovians). Credit: spiff.rit.edu

Within the Solar System, four Jovian planets exist – Jupiter, Saturn, Uranus and Neptune. A planet designated as Jovian is hence a gas giant, composed primarily of hydrogen and helium gas with varying degrees of heavier elements. In addition to having large systems of moons, these planets each have their own ring systems as well.

Another common feature of gas giants is their lack of a surface, at least when compared to terrestrial planets. In all cases, scientists define the “surface” of a gas giant (for the sake of defining temperatures and air pressure) as being the region where the atmospheric pressure exceeds one bar (the pressure found on Earth at sea level).

Structure and Composition:

In all cases, the gas giants of our Solar System are composed primarily of hydrogen and helium with the remainder being taken up by heavier elements. These elements correspond to a structure that is differentiated between an outer layer of molecular hydrogen and helium that surrounds a layer of liquid (or metallic) hydrogen or volatile elements, and a probable molten core with a rocky composition.

Due to difference in their structure and composition, the four gas giants are often differentiated, with Jupiter and Saturn being classified as “gas giants” while Uranus and Neptune are “ice giants”. This is due to the fact that Neptune and Uranus have higher concentrations of methane and heavier elements  – like oxygen, carbon, nitrogen, and sulfur – in their interior.

These cut-aways illustrate interior models of the giant planets. Jupiter is shown with a rocky core overlaid by a deep layer of metallic hydrogen. Credit: NASA/JPL
Interior models of the giant planets, showing rocky cores overlaid by solid and gaseous envelopes. Credit: NASA/JPL

In stark contrast to the terrestrial planets, the density of the gas giants is slightly greater than that of water (1 g/cm³). The one exception to this is Saturn, where the mean density is actually lower than water (0.687 g/cm3). In all cases, temperature and pressure increase dramatically the closer one ventures into the core.

Atmospheric Conditions:

Much like their structures and compositions, the atmospheres and weather patterns of the four gas/ice giants are quite similar. The primary difference is that the atmospheres get progressively cooler the farther away they are from Sun. As a result, each Jovian planet has distinct cloud layers who’s altitudes are determined by their temperatures, such that the gases can condense into liquid and solid states.

In short, since Saturn is colder than Jupiter at any particular altitude, its cloud layers occur deeper within it’s atmosphere. Uranus and Neptune, due to their even lower temperatures, are able to hold condensed methane in their very cold tropospheres, whereas Jupiter and Saturn cannot.

The presence of this methane is what gives Uranus and Neptune their hazy blue color, where Jupiter is orange-white in appearance due to the intermingling of hydrogen (which gives off a red appearance), while the upwelling of phosphorus, sulfur, and hydrocarbons yield spotted patches areas and ammonia crystals create white bands.

Shortly after forming, Jupiter was slowly pulled toward the sun. Saturn was also pulled in and eventually, their fates became linked. When Jupiter was about where Mars is now, the pair turned and moved away from the sun. Scientists have referred to this as the "Grand Tack," a reference to the sailing maneuver. Credit: NASA/GSFC
Jupiter and Saturn have similar appearances, owing to their similar compositions and atmospheres. Credit: NASA/GSFC

The atmosphere of Jupiter is classified into four layers based on increasing altitude: the troposphere, stratosphere, thermosphere and exosphere. Temperature and pressure increase with depth, which leads to rising convection cells emerging that carry with them the phosphorus, sulfur, and hydrocarbons that interact with UV radiation to give the upper atmosphere its spotted appearance.

Saturn’s atmosphere is similar in composition to Jupiter’s. Hence why it is similarly colored, though its bands are much fainter and are much wider near the equator (resulting in a pale gold color). As with Jupiter’s cloud layers, they are divided into the upper and lower layers, which vary in composition based on depth and pressure. Both planets also have clouds composed of ammonia crystals in their upper atmospheres, with a possible thin layer of water clouds underlying them.

Uranus’ atmosphere can be divided into three sections – the innermost stratosphere, the troposphere, and the outer thermosphere. The troposphere is the densest layer, and also happens to be the coldest in the solar system. Within the troposphere are layers of clouds, with methane clouds on top, ammonium hydrosulfide clouds, ammonia and hydrogen sulfide clouds, and water clouds at the lowest pressures.

Next is the stratosphere, which contains ethane smog, acetylene and methane, and these hazes help warm this layer of the atmosphere. Here, temperatures increase considerably, largely due to solar radiation. The outermost layer (the thermosphere and corona) has a uniform temperature of 800-850 (577 °C/1,070 °F), though scientists are unsure as to the reason.

Uranus and Neptune, the Solar System’s ice giant planets. (Images from Wikipedia.)
Uranus and Neptune, the Solar System’s ice giant planets. Credit: Wikipedia Commons

This is something that Uranus shares with Neptune, which also experiences unusually high temperatures in its thermosphere (about 750 K (476.85 °C/890 °F). Like Uranus, Neptune is too far from the Sun for this heat to be generated through the absorption of ultraviolet radiation, which means another heating mechanism is involved.

Neptune’s atmosphere is also predominantly hydrogen and helium, with a small amount of methane. The presence of methane is part of what gives Neptune its blue hue, although Neptune’s is darker and more vivid. Its atmosphere can be subdivided into two main regions: the lower troposphere (where temperatures decrease with altitude), and the stratosphere (where temperatures increase with altitude).

The lower stratosphere is believed to contain hydrocarbons like ethane and ethyne, which are the result of methane interacting with UV radiation, thus producing Neptune’s atmospheric haze. The stratosphere is also home to trace amounts of carbon monoxide and hydrogen cyanide, which are responsible for Neptune’s stratosphere being warmer than that of Uranus.

Weather Patterns:

Like Earth, Jupiter experiences auroras near its northern and southern poles. But on Jupiter, the auroral activity is much more intense and rarely ever stops. These are the result of Jupiter’s intense radiation, it’s magnetic field, and the abundance of material from Io’s volcanoes that react with Jupiter’s ionosphere.

Reprocessed view by Bjorn Jonsson of the Great Red Spot taken by Voyager 1 in 1979 reveals an incredible wealth of detail.
Reprocessed view by Bjorn Jonsson of the Great Red Spot taken by Voyager 1 in 1979 reveals an incredible wealth of detail. Credit: NASA/JPL

Jupiter also experiences violent weather patterns. Wind speeds of 100 m/s (360 km/h) are common in zonal jets, and can reach as high as 620 kph (385 mph). Storms form within hours and can become thousands of km in diameter overnight. One storm, the Great Red Spot, has been raging since at least the late 1600s.

The storm has been shrinking and expanding throughout its history; but in 2012, it was suggested that the Giant Red Spot might eventually disappear. Jupiter also periodically experiences flashes of lightning in its atmosphere, which can be up to a thousand times as powerful as those observed here on the Earth.

Saturn’s atmosphere is similar, exhibiting long-lived ovals now and then that can be several thousands of kilometers wide. A good example is the Great White Spot (aka. Great White Oval), a unique but short-lived phenomenon that occurs once every 30 Earth years. Since 2010, a large band of white clouds called the Northern Electrostatic Disturbance have been observed enveloping Saturn, and is believed to be followed by another in 2020.

The winds on Saturn are the second fastest among the Solar System’s planets, which have reached a measured high of 500 m/s (1800 km/h). Saturn’s northern and southern poles have also shown evidence of stormy weather. At the north pole, this takes the form of a persisting hexagonal wave pattern measuring about 13,800 km (8,600 mi) and rotating with a period of 10h 39m 24s.

Saturn makes a beautifully striped ornament in this natural-color image, showing its north polar hexagon and central vortex (Credit: NASA/JPL-Caltech/Space Science Institute)
Saturn makes a beautifully striped ornament in this natural-color image, showing its north polar hexagon and central vortex. Credit: NASA/JPL-Caltech/Space Science Institute

The south pole vortex apparently takes the form of a jet stream, but not a hexagonal standing wave. These storms are estimated to be generating winds of 550 km/h, are comparable in size to Earth, and believed to have been going on for billions of years. In 2006, the Cassini space probe observed a hurricane-like storm that had a clearly defined eye. Such storms had not been observed on any planet other than Earth – even on Jupiter.

Uranus’s weather follows a similar pattern where systems are broken up into bands that rotate around the planet, which are driven by internal heat rising to the upper atmosphere. Winds on Uranus can reach up to 900 km/h (560 mph), creating massive storms like the one spotted by the Hubble Space Telescope in 2012. Similar to Jupiter’s Great Red Spot, this “Dark Spot” was a giant cloud vortex that measured 1,700 kilometers by 3,000 kilometers (1,100 miles by 1,900 miles).

Because Neptune is not a solid body, its atmosphere undergoes differential rotation, with its wide equatorial zone rotating slower than the planet’s magnetic field (18 hours vs. 16.1 hours). By contrast, the reverse is true for the polar regions where the rotation period is 12 hours. This differential rotation is the most pronounced of any planet in the Solar System, and results in strong latitudinal wind shear and violent storms.

Reconstruction of Voyager 2 images showing the Great Black spot (top left), Scooter (middle), and the Small Black Spot (lower right). Credit: NASA/JPL
Reconstruction of Voyager 2 images showing the Great Dar Spot (top left), Scooter (middle), and the Small Dark Spot (lower right). Credit: NASA/JPL

The first to be spotted was a massive anticyclonic storm measuring 13,000 x 6,600 km and resembling the Great Red Spot of Jupiter. Known as the Great Dark Spot, this storm was not spotted five later (Nov. 2nd, 1994) when the Hubble Space Telescope looked for it. Instead, a new storm that was very similar in appearance was found in the planet’s northern hemisphere, suggesting that these storms have a shorter life span than Jupiter’s.

Exoplanets:

Due to the limitations imposed by our current methods, most of the exoplanets discovered so far by surveys like the Kepler space observatory have been comparable in size to the giant planets of the Solar System. Because these large planets are inferred to share more in common with Jupiter than with the other giant planets, the term “Jovian Planet” has been used by many to describe them.

Many of these planets, being greater in mass than Jupiter, have also been dubbed as “Super-Jupiters” by astronomers. Such planets exist at the borderline between planets and brown dwarf stars, the smallest stars known to exist in our Universe. They can be up to 80 times more massive than Jupiter but are still comparable in size, since their stronger gravity compresses the material into an ever denser, more compact sphere.

Artist's concept of "hot Jupiter" exoplanet HD 149026b (NASA/JPL-Caltech)
Artist’s concept of the “Hot Jupiter” exoplanet HD 149026b. Credit: NASA/JPL-Caltech

Those Super-Jupiters that have distant orbits from their parent stars are known as “Cold Jupiters”, whereas those that have close orbits are called “Hot Jupiters”. A surprising number of Hot Jupiters have been observed by exoplanet surveys, due to the fact that they are particularly easy to spot using the Radial Velocity method – which measures the oscillation of parent stars due to the influence of their planets.

In the past, astronomers believed that Jupiter-like planets could only form in the outer reaches of a star system. However, the recent discovery of many Jupiter-sized planets orbiting close to their stars has cast doubt on this. Thanks to the discovery of Jovians beyond our Solar System, astronomers may be forced to rethink our models of planetary formation.

Since Galileo first observed Jupiter through his telescope, Jovian planets have been an endless source of fascination for us. And despite many centuries of research and progress, there are still many things we don’t know about them. Our latest effort to explore Jupiter, the Juno Mission, is expected to produce some rather interesting finds. Here’s hoping they bring us one step closer to understanding those darn Jovians!

We have written many interesting articles about gas giants here at Universe Today. Here’s the Solar System Guide, The Outer Planets, What’s Inside a Gas Giant?, and Which Planets Have Rings?

For more information, check out NASA’s Solar System Exploration page and Science Daily’s the Jovian planets.

Astronomy Cast has a number of episodes on the Jovian planets, including Episode 56: Jupiter.

Posted on by Evan Gough

Juno and the Deep Space Network: Bringing The Data Home

NASA's Deep Space Network is responsible for communicating with Juno as it explores Jupiter. Pictured is the Goldstone facility in California, one of three facilities that make up the Network. Image: NASA/JPL
NASA's Deep Space Network is responsible for communicating with spacecraft. Pictured is the Goldstone facility in California, one of three facilities that make up the Network. Image: NASA/JPL

The much-anticipated arrival of NASA’s Juno spacecraft at Jupiter is almost here. Juno will answer many questions about Jupiter, but at the cost of a mission profile full of challenges. One of those challenges is communicating with Juno as it goes about its business in the extreme radiation environment around Jupiter. Communications with Juno rely on a network of radio dishes in strategic locations around the world, receivers cooled to almost absolute zero, and a team of dedicated people.

The task of communicating with Juno falls to NASA’s Deep Space Network (DSN), a system of three facilities around the world whose job it is to communicate with all of the spacecraft that venture outside Earth’s vicinity. That network is in the hands of Harris Corporation, experts in all sorts of communications technologies, who are contracted to run these crucial facilities.

The person responsible is Sonny Giroux, DSN Program Manager at Harris. In an interview with Universe Today, Sonny explained how the DSN works, and describes some of the challenges the Juno mission poses.

“The network itself consists of three primary communication facilities; one in Goldstone, California, out in the middle of the Mojave Desert. The other facility is in Madrid Spain, and the third is in Canberra Australia. These three facilities are separated by about 120 degrees, which means that any spacecraft that’s out there is capable of communicating with Earth at any point in time,” said Giroux.

Deep Space Network facilities are positioned 120 degrees apart to give total sky coverage. Image: NASA/JPL
Deep Space Network facilities are positioned 120 degrees apart to give total sky coverage. Image: NASA/JPL

“Each facility has several antennae, the largest of which is 70 m in diameter, about the size of a football field. These antennae can be aimed at any angle. Then there are smaller antennae at 34 m in size, and we have a number of those at each complex.”

According to Giroux, the dishes can work independently, or be arrayed together, depending on requirements. At the DSN website, you can see which antenna is communicating with which of NASA’s missions at any time.

At the Deep Space Network's website, you can see which of the network's dishes are communicating with which spacecraft. Image: NASA/JPL/DSN
At the Deep Space Network’s website, you can see which of the network’s dishes are communicating with which spacecraft. During Juno’s mission, you can expect to see its name beside many of the dishes. Image: NASA/JPL/DSN

Juno is a complex mission with a dynamic orbit, and Jupiter itself is an extreme radiation environment. Juno will have to weave its way through Jupiter’s radiation belts in its polar orbit. According to Giroux, this creates additional communication problems for the DSN.

“As Juno goes into its orbital insertion phase, the spacecraft will have to turn away from Earth. Our signal strength will drop dramatically,” Giroux said. “In order to capture the data that Juno is going to send, we’re going to array all of our antennae at Goldstone and Canberra together.”

Juno's orbit around Jupiter will be highly elliptical as it contends with Jupiter's powerful radiation belts. Image: NASA/JPL
Juno’s orbit around Jupiter will be highly elliptical as it contends with Jupiter’s powerful radiation belts. Image: NASA/JPL

This means that a total of 9 antennae will be arrayed in two groups to communicate with Juno. The 4 dishes at the Canberra, Australia site will be arrayed together, and the 5 dishes at the Goldstone, California site will be arrayed together.

This combined strength is crucial to the success of Juno during JOI (Juno Orbital Insertion.) Said Giroux, “We need to bring Juno’s signal strength up to the maximum amount that we can. We need to know what phases Juno is in as it executes its sequence.”

“We’ve never arrayed all of our antennae together like this. This is a first for Juno.”

This combined receiving power is a first for the DSN, and another first for the Juno mission. “We’ve never arrayed all of our antennae together like this,” said Giroux. “This is a first for Juno. We’ve done a couple together before for a spacecraft like Voyager, which is pretty far out there, but never all of them like this. In order to maximize our success with Juno, we’re arraying everything. It will be the first time in our history that we’ve had to array together all of our assets.”

Arraying multiple dishes together provides another benefit too, as Giroux told us. “The DSN is able to have two centres view the spacecraft at the same time. If one complex goes down for whatever reason, we would have the other one still available to communicate with the spacecraft.”

The most visible part of the DSN are the antennae themselves. But the electronics at the heart of the system are just as important. And they’re unique in the world, too.

“We cool them down to almost absolute zero to remove all of the noise out.”

“We have very specialized receivers that are built for the DSN. We cool them down to almost absolute zero to remove all of the noise out. That allows us to really focus on the signal that we’re looking for. These are unique to DSN,” said Giroux.

Juno itself has four different transmitters on-board. Some are able to transmit a lot of data, and some can transmit less. These will be active at different times, and form part of the challenge of communicating with Juno. Giroux told us, “Juno will be cycling through all four as it performs its insertion and comes back out again on the other side of the planet.”

“We just get the ones and zeroes…”

The DSN is a communications powerhouse, the most powerful tool ever devised for communicating in space. But it doesn’t handle the science. “DSN for the most part will receive whatever the spacecraft is sending to us. We just get the ones and zeroes and relay that data over to the mission. It’s the mission that breaks that down and turns it into science data.”

The three facilities that make up the DSN. Each is separated by 120 degrees. Image: NASA/JPL
The three facilities that make up the DSN. Each is separated by 120 degrees. Image: NASA/JPL

Juno will be about 450 million miles away at Jupiter, which is about a 96 minute round trip for any signal. That great distance means that Juno’s signal strength is extremely weak. But it won’t be the weakest signal that the DSN contends with. A testament to the strength of the DSN is the fact that it’s still receiving transmissions from the Voyager probes, which are transmitting at miniscule power levels. According to Giroux, “Voyager is at a billionth of a billionth of a watt in terms of its signal strength.”

Juno is different than other missions like New Horizons and Voyager 1 and 2. Once Juno is done, it will plunge into Jupiter and be destroyed. So all of its data has to be captured quickly and efficiently. According to Giroux, that intensifies the DSN’s workload for the Juno mission.

“Juno is different. We’ve got to make sure to capture that data regularly.”

“Juno has a very defined mission length, with start and stop dates. It will de-orbit into Jupiter when it’s finished its science phase. That’s different than other missions like New Horizons where it has long periods where its able to download all of the data it’s captured. Juno is different. We’ve got to make sure to capture that data regularly. After JOI we’ll be in constant communication with Juno to make sure that’s happening.”

To whet our appetites, the ESO has released these awesome IR images of Jupiter, taken by the VLT. Credit: ESO
In preparation for the arrival of Juno, the ESO’s released stunning IR images of Jupiter, taken by the VLT. Credit: ESO

The next most important event in Juno’s mission is its orbital insertion around Jupiter, and Giroux and the team are waiting for that just like the rest of us are. “Juno’s big burn as it slows itself enough to be captured by Jupiter is a huge milestone that we’ll be watching for,” said Giroux.

The first signal that the DSN receives will be a simple three second beep. “Confirmation of the insertion will occur at about 9:40 p.m.,” said Giroux. That signal will have been sent about 45 minutes before that, but the enormous distance between Earth and Jupiter means a long delay in receiving it. But once we receive it, it will tell us that Juno has finished firing its engine for orbital insertion. Real science data, including images of Jupiter, will come later.

“We want to see a successful mission as much as anybody else.”

All of the data from the DSN flows through the nerve center at NASA’s Jet Propulsion Laboratory. When the signal arrives indicating that Juno has fired its engines successfully, Giroux and his team will be focussed on that facility, where news of Juno’s insertion will first be received. And they’ll be as excited as the rest of us to hear that signal.

“We want to see a successful mission as much as anybody else. Communicating with spacecraft is our business. We’ll be watching the same channels and websites that everybody else will be watching with bated breath,” said Giroux.

“Its great to be a part of the network. It’s pretty special.”

Posted on by Evan Gough

Returned Samples Of Asteroid Itokawa Show Violent 4.5 Billion Year History

The surface patterns on one of the microscopic dust particles from asteroid Itokawa. Image: JAXA
The surface patterns on one of the microscopic dust particles from asteroid Itokawa. Image: JAXA

In 2003, the Japanese Aerospace Exploration Agency (JAXA) launched the Hayabusa probe. Its mission was to rendezvous with asteroid 25143 Itokawa in 2005. Once there, it studied a number of things about Itokawa, including its shape, topography, composition, colour, spin, density, and history. But the most exciting part of its mission was to collect samples from the asteroid and return them to Earth.

The mission suffered some complications, including the failure of Minerva, Hayabusa’s detachable mini-lander. But Hayabusa did land on the asteroid, and it did collect some samples; tiny grains of material from the surface of Itokawa. This was the first time a mission had landed somewhere and returned samples, other than missions to the Moon.

The Hayabusa spacecraft burned up on re-entry into Earth's atmosphere, but the capsule containing the samples survived. The glowing piece on the bottom front of the debris stream is the sample capsule. Image: NASA Ames, Public Domain
The Hayabusa spacecraft burned up on re-entry into Earth’s atmosphere, but the capsule containing the samples survived. The glowing piece on the bottom front of the debris stream is the sample capsule. Image: NASA Ames, Public Domain

Once the collected grains made it back to Earth in 2010, and were confirmed to be from the asteroid, scientists got excited. These grains would be key to helping understand the early Solar System when the planetary bodies were formed. And they have revealed a sometimes violent history going back 4.5 billion years.

The grains themselves are truly microscopic, at just over 10 micrometers in size. The marks and surface patterns on them are measured in nanometers. Initially, all the marks on the surfaces of the particles were thought to be of one type. But the team behind the study used electron microscopes and X-Ray Microtomography to reveal four different types of patterns on their surfaces.

One 4.5 billion year old pattern shows crystallization from intense heat. At this time period, Itokawa was part of a larger asteroid. The second pattern indicates a collision with a meteor about 1.3 billion years ago. Another pattern was formed by exposure to the solar wind between 1 million and 1,000 years ago. A fourth pattern detected by scientists shows that the particles have been rubbing against each other.

The team has concluded that Itokawa didn’t always exist in its current shape and form. When it was formed over 4 billion years ago, it was about 40 times bigger than it is now. That parent body was destroyed, and the researchers think that Itokawa re-formed from fragments of the parent body.

If there is still any lingering doubt about the violent nature of the Solar System’s history, the grains from Itokawa help dispel it. Collision, fragmentation, bombardments, and of course solar wind, seem to be the norm in our Solar System’s history.

The return of these samples was a bit of a happy accident. The sample collection mechanism on Hayabusa suffered a failure, and the returned dust grains were actually kicked up by the landing of the probe, and some ended up in the sample capsule.

For their part, JAXA has already launched Hayabusa’s successor, Hayabusa 2. It was launched in December 2014, and is headed for asteroid 162173 Ryugu. It should reach its destination in July 2018, and spend a year and a half there. Hayabusa 2 is also designed to collect asteroid samples and return them to Earth, this time using an explosive device to dig into the asteroid’s surface for a sample. Hayabusa 2 should return to Earth in December 2020.

An artist's image of Hayabusa leaving Earth. Image credit: JAXA
An artist’s image of Hayabusa leaving Earth. Image credit: JAXA

Hayabusa suffered several failures, including the failure of its mini-lander, problems with sample collection, and it even suffered damaged to its solar panels caused by a solar flare, which reduced its power and delayed its arrival at Itokawa. Yet it still ended up being a success in the end.

If Hayabusa 2 can avoid some of these problems, who knows what we may learn from more intentional samples. Sample missions are tricky and complex. If Hayabusa can return samples, it would be only the fourth body to have samples successfully returned to Earth, including the Moon, asteroid Itokawa, and comet Wild 2.

Posted on by Evan Gough

Earth Has An Almost-Moon

Earth has a new quasi-moon: an asteroid called 2016 H03. (Not shown) Image: NASA
Earth has a new quasi-moon: an asteroid called 2016 H03. (Not shown) Image: NASA

Earth has a small companion that NASA is calling an almost-Moon. The small asteroid, called 2016 H03, isn’t quite a moon because it’s actually orbiting the Sun. In its orbit around the Sun, it spends about half of its time closer to the Sun than the Earth.

2016 H03 is called a “quasi-moon” or a “near-Earth companion”. It doesn’t quite qualify as a moon because of its orbit.

Paul Chodas is the manager of NASA’s Center for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in Pasadena, California. He had this to say about 2016 H03: “Since 2016 HO3 loops around our planet, but never ventures very far away as we both go around the sun, we refer to it as a quasi-satellite of Earth.”

2016 H03’s orbit is tilted relative to Earth’s, and it passes through the plane of Earth’s orbit. Over the decades, it also performs a slow, back and forth twist. NASA describes 2016 H03’s orbit as a game of leap frog.

“The asteroid’s loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth’s gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon,” said Chodas. “The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon. In effect, this small asteroid is caught in a little dance with Earth.”

Earth’s little quasi-moon has been in its stable orbit for about a century, according to calculations, though it was only spotted on April 27th, 2016, by the Pan-STARRS 1 asteroid survey telescope in Hawaii. Pan-STARRS 1 is operated by the University of Hawaii’s Institute for Astronomy and NASA’s Planetary Defense Coordination Office. (Did you know we had a Planetary Defense Coordination Office?)

2016 H03 is small. It’s exact size has not been established, but it’s between 40 and 100 meters (120 and 300 ft.) It’s been around a century, and calculations say it will be around for centuries more.

2016 H03 is not quite unique. Earth has had other dance partners like it.

“One other asteroid — 2003 YN107 — followed a similar orbital pattern for a while over 10 years ago, but it has since departed our vicinity. This new asteroid is much more locked onto us. Our calculations indicate 2016 HO3 has been a stable quasi-satellite of Earth for almost a century, and it will continue to follow this pattern as Earth’s companion for centuries to come,” said Chudas.

NASA tracks thousands of NEOs and assesses their risk of collision with Earth. Though 2016 H03 is an interesting specimen because of its orbit, it poses no threat to Earth.

Posted on by Evan Gough

470 Million Year Old Meteorite Discovered In Swedish Quarry

Osterplana 65, the meteorite at the heart of a mystery. This meteorite is different than the thousands of other meteorites in collections around the world. Image: Birger Schmitz
Osterplana 65, the meteorite at the heart of a mystery. This meteorite is different than the thousands of other meteorites in collections around the world. Image: Birger Schmitz

470 million years ago, somewhere in our Solar System, there was an enormous collision between two asteroids. We know this because of the rain of meteorites that struck Earth at that time. But inside that rain of meteorites, which were all of the same type, there is a mystery: an oddball, different from the rest. And that oddball could tell us something about how rocks from space can change ecosystems, and allow species to thrive.

This oddball meteorite has a name: Osterplana 65. It’s a fossilized meteorite, and it was found in a limestone quarry in Sweden. Osterplana 65 fell to Earth some 470 mya, during the Ordovician period, and sank to the bottom of the ocean. There, it became sequestered in a bed of limestone, itself created by the sea-life of the time.

The Ordovician period is marked by a couple thing: a flourishing of life similar to the Cambrian period that preceded it, and a shower of meteors called the Ordovician meteor event. There is ample evidence of the Ordovician meteor event in the form of meteorites, and they all conform to similar chemistry and structure. So it’s long been understood that they all came from the same parent body.

The collision that caused this rain of meteorites had to have two components, two parent bodies, and Osterplana 65 is evidence that one of these parent bodies was different. In fact, Ost 65 represents a so far unknown type of meteorite.

The faint grey lines in this electron image of Ost 65 are called "shock deformation lamellae" and they are evidence that Ost 65 was the result of a collision. Image: B. Schmidt
The faint grey lines in this electron image of Ost 65 are called “shock deformation lamellae” and they are evidence that Ost 65 was the result of a collision. Image: B. Schmidt

The study that reported this finding was published in Nature on June 14 2016. As the text of the study says, “Although single random meteorites are possible, one has to consider that Öst 65 represents on the order of one per cent of the meteorites that have been found on the mid-Ordovician sea floor. “It goes on to say, “…Öst 65 may represent one of the dominant types of meteorites arriving on Earth 470 Myr ago.”

The discovery of a type of meteorite falling on Earth 470 mya, and no longer falling in our times, is important for a couple reasons. The asteroid that produced it is probably no longer around, and there is no other source for meteorites like Ost 65 today.

The fossil record of a type of meteorite no longer in existence may help us unravel the story of our Solar System. The asteroid belt itself is an ongoing evolution of collision and destruction. It seems reasonable that some types of asteroids that were present in the earlier Solar System are no longer present, and Ost 65 provides evidence that that is true, in at least one case.

Ost 65 shows us that the diversity in the population of meteorites was greater in the past than it is today. And Ost 65 only takes us back 470 mya. Was the population even more diverse even longer ago?

The Earth is largely a conglomeration of space rocks, and we know that there are no remnants of these Earthly building blocks in our collections of meteorites today. What Ost 65 helps prove is that the nature of space rock has changed over time, and the types of rock that came together to form Earth are no longer present in space.

Ost 65 was found in amongst about 100 other meteorites, which were all of the same type. It was found in the garbage dump part of the quarry. It’s presence is a blemish on the floor tiles that are cut at the quarry. Study co-author Birgen Schmitz told the BBC in an interview that “It used to be that they threw away the floor tiles that had ugly black dots in them. The very first fossil meteorite we found was in one of their dumps.”

According to Schmitz, he and his colleagues have asked the quarry to keep an eye out for these types of defects in rocks, in case more of them are fossilized meteorites.

Finding more fossilized meteorites could help answer another question that goes along with the discovery of Ost 65. Did the types and amounts of space rock falling to Earth at different times help shape the evolution of life on Earth? If Ost 65 was a dominant type of meteorite falling to Earth 470 mya, what effect did it have? There appear to be a confounding number of variables that have to be aligned in order for life to appear and flourish. A shower of minerals from space at the right time could very well be one of them.

Whether that question ever gets answered is anybody’s guess at this point. But Ost 65 does tell us one thing for certain. As the text of the study says, “Apparently there is potential to reconstruct important aspects of solar-system history by looking down in Earth’s sediments, in addition to looking up at the skies.”

Posted on by Evan Gough

Mars Stink To Be Duplicated For Earthbound Humans

Thanks to the rovers Spirit, Opportunity, and Curiosity, everyone knows what Mars looks like. But what does it smell like? Image: NASA/JPL-Caltech/MSSS
Thanks to the rovers Spirit, Opportunity, and Curiosity, everyone knows what Mars looks like. But what does it smell like? Image: NASA/JPL-Caltech/MSSS

Intellectual curiosity is a great gift. It’s fulfilling to ponder the great questions of existence: Will the Universe die of heat death after it’s expanded for billions and billions (and billions) more years? Is there something outside of our Universe? What’s on the other side of a black hole?…and…What does Mars smell like?

Seriously.

What may seem to be a frivolous question at first is actually quite interesting once your intellectual curiosity is engaged. The Martian atmosphere itself is much different than Earth’s. Our various robotic visitors to Mars have revealed an atmosphere rich in carbon dioxide (96%). Not much to smell there. But the surface of Mars is also much different than Earth, and contains sulfur, acids, magnesium, iron and chlorine compounds. What might that smell like?

We know that odours have a powerful effect on memory. How might colonists respond to an odour so different from what they’re used to? How might they respond to the odour of Mars once they’ve returned to Earth after a Mars mission? Recreating the smell of Mars for returning colonists might yield interesting results.

The olfactory nerve has a powerful connection to areas of the brain involved in arousal and attention. Can this connection be exploited to help Martian colonists? Image: Patrick J. Lynch CC BY 2.5
The olfactory nerve has a powerful connection to areas of the brain involved in arousal and attention. Can this connection be exploited to help Martian colonists? Image: Patrick J. Lynch CC BY 2.5

Obviously, colonists wouldn’t be breathing the Martian atmosphere. But some essence of Mars would be present in their living quarters, most likely.

After walking on the Moon, Apollo astronauts noticed that they had tracked some Moon dust back into the lander with them. When they removed their helmets, they were able to smell the Moon: a spent gunpowder smell, or a wet ash smell like a campfire that had been put out. The same thing may happen on Mars, no matter how careful people are.

The International Space Station (ISS) has its own particular smell. According to NASA astronaut Don Pettit, the ISS smells like a combined machine shop/engine room/laboratory. But the ISS isn’t a colony, and it isn’t exposed to other worlds. Everything astronauts can smell inside the ISS they can smell back on Earth.

Mars is different. Not just the smell, but because it’s so far away. In the ISS, astronauts can look down and see Earth whenever they want. They can see their country of origin, and see familiar geography. On Mars, none of that is possible. Martians will be dealing with extreme isolation.

How this isolation might affect people spending long periods of time on Mars is an intriguing and important question. And how odors play a part in this is likewise intriguing.

The effects of social isolation are well-understood. It can lead to depression, insomnia, anxiety, fatigue, boredom and emotional instability. These are garden variety problems that everyone faces at some point, but added all together they’re a potent mix that could produce serious mental illness.

Add to that the fact that Martian colonists won’t even be able to see Earth, let alone the fact of the shrunken, pale Sun, and suddenly the psychological burden of colonizing Mars comes into sharper focus. It’ll take a multi-pronged approach to help colonists cope with all of this.

Part of this approach may involve recreating the smell of Mars and exposing colonists to it during their pre-colonization training. And thanks to a technology called “Headspace“, it may be possible to recreate the smell of Mars here on Earth. Spectroscopic measurements of the Martian atmosphere could be relayed back to Earth and the Martian aroma could be recreated in a lab.

Perhaps the smell of Mars can be used prior to departure to help inoculate colonists to some of the hazards of Martian isolation.

Who knows for sure? There may be an interesting revelation hidden in the smell of Mars. How that smell could be used to prepare colonists for their time on Mars, and how returning astronauts respond to the smell of Mars, recreated for them back on Earth, could tell us something important about how our brains work.

Intellectual curiosity says its worth pondering.

Posted on by Matt Williams

How Was the Solar System Formed? – The Nebular Hypothesis

Solar System Themed Products
Solar System Montage. Credit: science.nationalgeographic.com

Since time immemorial, humans have been searching for the answer of how the Universe came to be. However, it has only been within the past few centuries, with the Scientific Revolution, that the predominant theories have been empirical in nature. It was during this time, from the 16th to 18th centuries, that astronomers and physicists began to formulate evidence-based explanations of how our Sun, the planets, and the Universe began.

When it comes to the formation of our Solar System, the most widely accepted view is known as the Nebular Hypothesis. In essence, this theory states that the Sun, the planets, and all other objects in the Solar System formed from nebulous material billions of years ago. Originally proposed to explain the origin of the Solar System, this theory has gone on to become a widely accepted view of how all star systems came to be.

Nebular Hypothesis:

According to this theory, the Sun and all the planets of our Solar System began as a giant cloud of molecular gas and dust. Then, about 4.57 billion years ago, something happened that caused the cloud to collapse. This could have been the result of a passing star, or shock waves from a supernova, but the end result was a gravitational collapse at the center of the cloud.

From this collapse, pockets of dust and gas began to collect into denser regions. As the denser regions pulled in more and more matter, conservation of momentum caused it to begin rotating, while increasing pressure caused it to heat up. Most of the material ended up in a ball at the center while the rest of the matter flattened out into disk that circled around it. While the ball at the center formed the Sun, the rest of the material would form into the protoplanetary disc.

The planets formed by accretion from this disc, in which dust and gas gravitated together and coalesced to form ever larger bodies. Due to their higher boiling points, only metals and silicates could exist in solid form closer to the Sun, and these would eventually form the terrestrial planets of Mercury, Venus, Earth, and Mars. Because metallic elements only comprised a very small fraction of the solar nebula, the terrestrial planets could not grow very large.

In contrast, the giant planets (Jupiter, Saturn, Uranus, and Neptune) formed beyond the point between the orbits of Mars and Jupiter where material is cool enough for volatile icy compounds to remain solid (i.e. the Frost Line). The ices that formed these planets were more plentiful than the metals and silicates that formed the terrestrial inner planets, allowing them to grow massive enough to capture large atmospheres of hydrogen and helium. Leftover debris that never became planets congregated in regions such as the Asteroid Belt, Kuiper Belt, and Oort Cloud.

Artist's impression of the early Solar System, where collision between particles in an accretion disc led to the formation of planetesimals and eventually planets. Credit: NASA/JPL-Caltech
Artist’s impression of the early Solar System, where collision between particles in an accretion disc led to the formation of planetesimals and eventually planets. Credit: NASA/JPL-Caltech

Within 50 million years, the pressure and density of hydrogen in the center of the protostar became great enough for it to begin thermonuclear fusion. The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved. At this point, the Sun became a main-sequence star. Solar wind from the Sun created the heliosphere and swept away the remaining gas and dust from the protoplanetary disc into interstellar space, ending the planetary formation process.

History of the Nebular Hypothesis:

The idea that the Solar System originated from a nebula was first proposed in 1734 by Swedish scientist and theologian Emanual Swedenborg. Immanuel Kant, who was familiar with Swedenborg’s work, developed the theory further and published it in his Universal Natural History and Theory of the Heavens (1755). In this treatise, he argued that gaseous clouds (nebulae) slowly rotate, gradually collapsing and flattening due to gravity and forming stars and planets.

A similar but smaller and more detailed model was proposed by Pierre-Simon Laplace in his treatise Exposition du system du monde (Exposition of the system of the world), which he released in 1796. Laplace theorized that the Sun originally had an extended hot atmosphere throughout the Solar System, and that this “protostar cloud” cooled and contracted. As the cloud spun more rapidly, it threw off material that eventually condensed to form the planets.

This image from the NASA/ESA Hubble Space Telescope shows Sh 2-106, or S106 for short. This is a compact star forming region in the constellation Cygnus (The Swan). A newly-formed star called S106 IR is shrouded in dust at the centre of the image, and is responsible for the surrounding gas cloud’s hourglass-like shape and the turbulence visible within. Light from glowing hydrogen is coloured blue in this image. Credit: NASA/ESA
The Sh 2-106 Nebula (or S106 for short), a compact star forming region in the constellation Cygnus (The Swan). Credit: NASA/ESA

The Laplacian nebular model was widely accepted during the 19th century, but it had some rather pronounced difficulties. The main issue was angular momentum distribution between the Sun and planets, which the nebular model could not explain. In addition, Scottish scientist James Clerk Maxwell (1831 – 1879) asserted that different rotational velocities between the inner and outer parts of a ring could not allow for condensation of material.

It was also rejected by astronomer Sir David Brewster (1781 – 1868), who stated that:

“those who believe in the Nebular Theory consider it as certain that our Earth derived its solid matter and its atmosphere from a ring thrown from the Solar atmosphere, which afterwards contracted into a solid terraqueous sphere, from which the Moon was thrown off by the same process… [Under such a view] the Moon must necessarily have carried off water and air from the watery and aerial parts of the Earth and must have an atmosphere.”

By the early 20th century, the Laplacian model had fallen out of favor, prompting scientists to seek out new theories. However, it was not until the 1970s that the modern and most widely accepted variant of the nebular hypothesis – the solar nebular disk model (SNDM) – emerged. Credit for this goes to Soviet astronomer Victor Safronov and his book Evolution of the protoplanetary cloud and formation of the Earth and the planets (1972). In this book, almost all major problems of the planetary formation process were formulated and many were solved.

For example, the SNDM model has been successful in explaining the appearance of accretion discs around young stellar objects. Various simulations have also demonstrated that the accretion of material in these discs leads to the formation of a few Earth-sized bodies. Thus the origin of terrestrial planets is now considered to be an almost solved problem.

While originally applied only to the Solar System, the SNDM was subsequently thought by theorists to be at work throughout the Universe, and has been used to explain the formation of many of the exoplanets that have been discovered throughout our galaxy.

Problems:

Although the nebular theory is widely accepted, there are still problems with it that astronomers have not been able to resolve. For example, there is the problem of tilted axes. According to the nebular theory, all planets around a star should be tilted the same way relative to the ecliptic. But as we have learned, the inner planets and outer planets have radically different axial tilts.

Whereas the inner planets range from almost 0 degree tilt, others (like Earth and Mars) are tilted significantly (23.4° and 25°, respectively), outer planets have tilts that range from Jupiter’s minor tilt of 3.13°, to Saturn and Neptune’s more pronounced tilts (26.73° and 28.32°), to Uranus’ extreme tilt of 97.77°, in which its poles are consistently facing towards the Sun.

The latest list of potentially habitable exoplanets, courtesy of The Planetary Habitability Laboratory. Credit: phl.upr.edu
A list of potentially habitable exoplanets, courtesy of The Planetary Habitability Laboratory. Credit: phl.upr.edu

Also, the study of extrasolar planets have allowed scientists to notice irregularities that cast doubt on the nebular hypothesis. Some of these irregularities have to do with the existence of “hot Jupiters” that orbit closely to their stars with periods of just a few days. Astronomers have adjusted the nebular hypothesis to account for some of these problems, but have yet to address all outlying questions.

Alas, it seems that it questions that have to do with origins that are the toughest to answer. Just when we think we have a satisfactory explanation, there remain those troublesome issues it just can’t account for. However, between our current models of star and planet formation, and the birth of our Universe, we have come a long way. As we learn more about neighboring star systems and explore more of the cosmos, our models are likely to mature further.

We have written many articles about the Solar System here at Universe Today. Here’s The Solar System, Did our Solar System Start with a Little Bang?, and What was Here Before the Solar System?

For more information, be sure to check out the origin of the Solar System and how the Sun and planets formed.

Astronomy Cast also has an episode on the subject – Episode 12: Where do Baby Stars Come From?

Posted on by Evan Gough

Mars At Closest Point To Earth in 11 Years May 30, 2016

Mars in all its red-hued glory. Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Bell (ASU), and M. Wolff (Space Science Institute)
Mars in all its red-hued glory. Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Bell (ASU), and M. Wolff (Space Science Institute)

If you have a telescope, (What?! You don’t have one?) you’re in for a visual treat tonight. Mars will be at its closest point to Earth in 11 years on May 30. This event is worth checking out, whether with a telescope, astronomy binoculars, or online.

While today is when Mars is at its closest, you actually have a couple weeks to check this out, as the distance between Mars and Earth gradually becomes greater and greater. Today, Mars is 76 million kilometers (47.2 million miles) away, but up until June 12th it will still be no further than 77 million kilometers (48 million miles) away.

The furthest Mars can be from Earth is 401 million kilometers (249 million miles), when the two planets are on the opposite side of the Sun from each other.

For most of us with backyard ‘scopes, it’s difficult to make out much detail. You can see Mars, and at the most you can make out a polar cap. But it’s still fascinating knowing you’re looking at another planet, one that was totally unknowable for most humans who preceded us. A planet that we have rovers on, and that we have several craft in orbit around.

If you don’t have a scope, have no fear. There will be a flood of great astro-photos of Mars in the next few days. There are also options for live streaming feeds from powerful Earth-based telescopes.

The last time Mars was this close to Earth was 2005. A couple years before, the distance shrank to 55.7 million km (34.6 million miles.) That was the closest Mars and Earth have been in several thousand years. In 2018, the two planets will be nearly that close again.

This event is often called “opposition”, but it’s actually more correctly called “closest approach.” Opposition occurs a couple weeks before closest approach, when Mars is directly opposite the Sun.

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

But whether you call it opposition, or closest approach, the event itself is significant for more than just looking at it. Missions to Mars are planned when the two planets are close to each other. This reduces mission times drastically.

Mars Express, the mission being conducted by the European Space Agency (ESA) was launched in 2003, when the two planets were as close to each other as they’ve been in thousands of years. All missions to Mars can’t be so lucky, but they all strive to take advantage of the orbital cycles of the two planets, by nailing launch dates that work in our favour.

As for finding Mars in the night sky, it’s not that difficult. If you have clear skies where you are, Mars will appear as a bright, fire-yellow star.
“Just look southeast after the end of twilight, and you can’t miss it,” says Alan MacRobert, a senior editor of Sky & Telescope magazine, in a statement. “Mars looks almost scary now, compared to how it normally looks in the sky.”

This image shows how Mars appears at different times of the year in a typical backyard telescope. Image: NASA/JPL-Caltech
This image shows how Mars appears at different times of the year in a typical backyard telescope. Image: NASA/JPL-Caltech

Although Mars is the closest thing in the sky to Earth right now, other than the Moon, it isn’t the brightest thing in the night sky. That honour is reserved for Jupiter, even though it’s ten times further away. Jupiter is twenty times larger in diameter than Mars, so it reflects much more sunlight and appears much brighter. (Obviously, everything in the night sky pales in comparison to the Moon.)

The reason for such a variation in distances between the planets lies in their elliptical orbits around the Sun. There’s a great video showing how their orbits change the distance between the two planets, here.

If you don’t have a telescope, you can still check Mars out. Go to slooh.com to check out live feeds from a proper telescope.