The best info about space .

Space, the universe and everything

How the universe began

Whenever I look up at the sky at night and see the Milky Way I often wonder about the Big Bang. What I can't get my head around is how the process could go from nothing to the start of the Big Bang. How can one have nothing and then suddenly all the necessary materials that produced our universe? What alternatives are there for the big bang theory? I don't believe in creationism but cant get my head around all space, time and matter coming into being from a single point?

The reason people have problems understanding the Big Bang, is that they are imagining that space and time have always existed, like a picture frame ready for some painter to come along. They are trying to see the big bang "happening" within that frame. They are pretending that time stretches infinitely far back and that the big bang happened like a bomb going off.

In order to make any progress with understanding the origin of the universe (at least as much about the origin of the universe as we can squeeze out of cosmological observations and general relativity) we have to get rid of this eternal space and time idea. One simple way to remind ourself of this is the phrase: There was no time before time came into existence.

The big bang theory is a little like Darwiniam evolution. It is a theory which has been so successful that all competitors have been marginalised. So there really are no good alternatives. However, there are important pieces missing that aren't understood very well at all...and these are arguably the most important pieces. How did life begin? How did the universe begin?

Conservative versions of the "big bang theory" don't even discuss the origin of the universe...many scientists are content to discuss the big bang only so far as the observational evidence goes...and it goes back surprisingly far. But, as is always the case, it becomes more tenuous as we go further back. For example, we can study the production of helium in the universe during the first three minutes and we can test our predictions quite precisely. We can study the formation of the first atoms about 400,000 years after the big bang. To some extent we can even test theories about what happened after the first billionth of a billionth of a second. Our ideas about what happened earlier (or even whether it makes sense to talk about times earlier than that) should be approached with a healthy scepticism.

If you could find good evidence that some star or galaxy (or anything else) was older than the 13.7 billion year estimate for the age of the universe, you would have strong evidence against the big bang and you'd win a Nobel prize and alternatives to the big bang would be popping out everywhere. 

Zero-gravity birth

Are there any predictions of what will happen when people are born in zero or weaker gravity conditions eg will they be able to live on Earth after several years in such conditions.

Astronauts used to have large difficulties readjusting to earth's gravity after long duration space flights (imagine watching TV for a few weeks from a very soft couch and then trying to get up and walk around - you'd have difficulties too).

The best solution to these difficulties appears to be regular focused exercises that put stresses on bones and muscles in the way that earth's gravity does. This is what astronauts now do. I imagine that if a human or any other biped or quadruped was born in zero gravity and lived in it for a large fraction of its formative years without such focused exercise, some degree of walking impairment might be irreversible.

Is gravity faster than light?

Light travels at a finite speed (but nothing can travel faster than it). It takes light approximately eight minutes to travel from our Sun to Earth (1AU). But if the Sun were to disappear the gravitational effects would be felt instantly. Is all this true? If so does gravity travel faster than light?

No, gravity does not travel faster than light. The gravitational force also travels at the speed of light. This was postulated by Einstein, and was first measured in 2003 by scientists at National Radio Astronomy Observatory in Charlottesville, Virginia. Formally the effects of gravity are manifested through its effect on the shape of space-time, and this distortion moves at the speed of light. So if the Sun were to suddenly disappear then space-time would react to that at the speed of light and in about 8 minutes the Earth would head off in a straight line, along a tangent to its orbit at the time that the gravitational force from the Sun disappeared - ie about 8 mins after the Sun itself disappeared, and at the same time that things suddenly got very dark!

Gravitational influences also propagate at the speed of light. According to General Relativity, changes in distributions of mass produce gravity waves, which communicate the changes. There is currently a concerted effort to try to detect these waves experimentally.

Basically, if the Sun were to disappear, we would only know about it eight minutes later. 

Although gravitational waves have not yet been observed, we think that such a change in gravitation fields will travel in much the same way as light or other electromagnetic waves travel, and with the same speed. Thus it would be about eight minutes before we knew that the Sun's gravitational field has disappeared.

What the universe looks like now

If the light from stars and galaxies that we see (telescopes, Hubble or eyes) is from millions of years ago, what does the universe actually look like now and do we have any way of telling what that is?

This is a good question. It raises a subtle issue that we do not have to deal with on a daily basis, because of the speed of light being so fast. This is the issue of "simultaneity". How do two different people know that two events occurred *simultaneously*? Einstein told us that there is no preferred time, only time relative to an observer. So when the question asks "what does it look like now" we have to reply "according to who?" The concept of "now" is fuzzy!

It is true that when we look in the sky we see the stars etc as they were when the light left. This is also true when we look at our watch. We see the time when the light left the watch, not the time "now". But since these are so close together, we do not even consider that the times are different. But technically they are. And when you start dealing with huge distances, then it can be important.

So imagine looking at the binary star system alpha Centauri. It is about 4 light years away so we see the two stars as they were 4 years ago. How do they look now? Well - they look exactly as we see them! It depends on who is looking and how far away they are... Maybe we should ask "How are the stars arranged now?" Well, if you know the orbit, you can move them forward 4 years, and that is the position they have "now". But its almost meaningless, as you cannot see them in that position. Further, maybe some disaster occurred and the system has been destroyed! We simply do not know until the information (ie light in this case) gets to us. So what do we mean by "real position" and "now"? Until the information arrives, we simply cannot be sure! 

Lunar lifestyle

We are told Man is going back to the Moon and beyond, but has anyone yet thought of providing him with safe functional living quarters below ground? A thin walled space vehicle above ground will not protect Mankind from solar flares etc.

The surface of the Moon and Mars is largely blanketed by regolith, which is loose material like soil, sand, and gravel that can be easily excavated. There has been quite a lot of study into using Lunar and Martian regolith to provide radiation shielding. The advantage of this is that you can use local materials to construct the radiation shielding needed for long missions.

There are several ways that regolith could be used. The simplest is to bag it and drape the upper surfaces of your lunar or Martian station with these bags. Or you could erect a flat roof and spread a layer of regolith on this. Other suggestions include burying the entire Moon or Mars station by piling regolith over the top or digging a trench and placing your living modules in these before roofing these over and burying them in more regolith.

It might even be possible to use natural caves, such as lava tubes, as shelters, if these are in the right places and the right size and shape. Lava tubes, rather like those found in Queensland and Victoria, are believed to occur in several places on the Moon and Mars. As for using places like Coober Pedy as a way of learning how people might cope with living underground, I think this is an excellent idea.

What we can expect to see is the construction of bases using modules like those on the International Space Station. Radiation shielding will have to be improved. Coping with dusty places like the Moon and Mars will have its own challenges. Hazards may have to be diminished by limiting the duration of occupation. Not only the major space agencies but also the MARS Society is actively experimenting with such habitats and lifestyles, including here in Australia.

Moons with moons

Why don't moons have moons?

The Earth orbits the Sun, and so is a satellite of the Sun. The Moon orbits the Earth, and so is a satellite of a satellite. Even small asteroids orbiting the Sun can have other asteroids orbiting them (asteroid-moons). So, in theory, our Moon, or the moon of any other planet, could have its own moon: a moon-moon.

The orbit of such a moon-moon must lie within a certain restricted region around the primary moon, called the "Hill sphere". The size of the Hill sphere depends on the gravitational fields of all bodies in the system. Massive bodies (like Jupiter and Neptune) that are far from other massive objects will have the largest Hill spheres, and thus the largest regions in which stray objects could be "captured" into orbits to become moons.

Most moons are so small and orbit so close to their parent bodies that they have very small Hill spheres and thus very small regions in which moon-moons could exist. Even within this region, a moon-moon may not be long-lived. Tidal effects may distort the shape of the primary body, changing the gravitational force on the satellite and slowing it down or speeding it up. In many cases the satellite's orbit will decay: the moon-moon will either crash into its parent moon or be torn apart by tidal effects. Indeed, after an extremely long period of time, some of the moons in the Solar System are expected to crash into their parent planets. Perhaps one distant day a curious person will ask, "Why don't some planets have moons?" 

The Outerverse

If the universe is infinite and at the same time expanding, what is outside of our expanding universe? Is it finite or infinite?

The latest cosmological observations are consistent with the idea that the universe is spatially infinite (but the portion of it that we can see - the observable universe - is finite). The universe does not expand like a bomb into previously empty space. Astronomers casually say that distant galaxies are "receding" or "moving away" from us, but the galaxies are not travelling through space away from us. They are not fragments of a big bang bomb that blew up 14 billion years ago in a specific place.

Instead the space between the galaxies and us is expanding and the big bang happened everywhere 14 billion years ago. One way to imagine this is to consider an infinite rubber sheet. Draw a circle on the sheet to represent our observable universe. Draw lots of other circles anywhere you want on the sheet to represent other observable universes - they can overlap with our circle if you like. Now let the rubber sheet expand. All the circles will get bigger but they don't expand into previously empty space - all of space is expanding and this expansion does not require empty space on the outside (wherever that is) to expand into. When it expands, it does not claim previously unoccupied space from its surroundings. In Einstein's general theory of relativity, the foundation of modern cosmology, space can expand in this way as well as shrink and curve without being embedded in a higher-dimensional space. 

When we observe the Universe we find that it looks pretty much the same in all directions. We call this isotropy. Maps have been made of where galaxies reside in the nearby Universe, and these show that the Earth is not at the centre of the Universe. The Universe must therefore be isotropic around all points (ie homogeneous).

When these observed requirements of isotropy and homogeneity are put into the theory of General Relativity, a solution is found where space can expand (or contract). However this space is not thought of as expanding into something. In General Relativity space and time cannot be thought of separately as we do in everyday life. Rather space and time make up a 4-dimensional "space-time". Since its very hard to think in 4 dimensions we can consider the following simple analogy.

Take a balloon, and think of its surface as a two dimensional world (in analogy to our 3-d world). Things can move along the surface but not perpendicular to it. To an observer on the surface this world looks isotropic around every point, just like our universe. If the balloon is blown up, then the surface expands around all points, again just like our Universe. In this analogy the balloon is not expanding into space, but rather it is expanding in time. The balloon analogy represents a finite universe (since one can measure the area of the balloon). However General Relativity permits universes that are infinite as well. We believe our Universe is infinite in extent. 

Why doesn't the Earth 'capture' asteroids?

I read today about the impending near miss with the meteor/asteroid. Why doesn't the Earth's gravitational field capture these near miss satellites and why don't we have thousands of them orbiting the Earth? If the answer to my first question is that the orbits would decay and fall into the atmosphere to burn up, then why doesn't the Moon's orbit decay?

Whether or not a passing body can be captured into the Hill sphere (the gravitational sphere of influence around an astronomical body) depends on how fast it is travelling. Many fast-moving objects will be able to escape, although their trajectory may be altered by the "close" passage.

Our own Moon's orbit is actually expanding, not decaying. This is because the Earth rotates faster than the Moon orbits the Earth, so that the tides that the Moon raises on the Earth "lead" or are slightly "ahead of" the Moon, speeding it up. This allows the Moon to move to a larger orbit. 

Is there anybody out there?

What is the chance of there being life and then intelligent life in our galaxy or the whole Universe?

As our knowledge about types and numbers of planets in the galaxy improves, the answer to this question is becoming more and more dependent on philosophy (how does one define "intelligent"?) and on our knowledge of biology (under what conditions can life thrive?) than on our knowledge of other planetary systems.

What we do know is that at least a few percent of all stars like our own Sun have planets. Some of these planets are larger than Jupiter and made of gas. Others are a few times the mass of the Earth, and probably rocky or icy worlds. Astronomers doubt that any of the 194 planets now known orbiting other stars are likely to support liquid water at their surface. Liquid water is sometimes taken to be a condition for "life as we know it." (Of course, it is quite possible that nature includes "life as we don't know it"!)

Planets similar to our Earth are difficult to detect, and we have only just begun to search with adequate tools. Within the next five to 20 years, we should have a good estimate of the fraction of normal stars with vaguely Earth-like planets. Given the huge number of stars in our galaxy (tens of billions) and the similar number of galaxies in the Universe, we can probably be certain that a large number, perhaps billions, of other Earth-like planets exist somewhere in the cosmos. The question, for biologists and philosophers, is then: "Could any of these planets harbour intelligent life?" In the absence of evidence to the contrary, safe money may be on "yes." 

When the Sun dies

Assuming that the reaction that makes the Sun work was to stop, how long would it take to cool down and what would be left?

The Sun is powered by the fusion of hydrogen. If this were to suddenly stop, then the Sun would contract on itself, just as it did earlier in its life, when it contracted from a large gas cloud to a star. It was only the start of hydrogen fusion that halted this contraction, and if we somehow turn off the fusion then the contraction will continue.

This contraction will release gravitational energy and there would be no noticeable change in the brightness of the Sun for quite some time - something like a few million years! But it would gradually change, and as it contracts it uses up the gravitational energy available to it, and it would eventually dim and disappear, after maybe 50 million years, as a faint ball of gas not unlike a very massive brown dwarf. 

Due to the extreme pressures and temperatures at its core, the Sun can fuse hydrogen into helium and other elements, releasing energy. The extreme conditions are due to the outer layers of the Sun squeezing the core and making fusion possible. Strangely, if we turned off nuclear fusion, the temperature of the core would increase. The radiation produced by fusion pushes on the outer layers and acts to reduce the central pressure - without the radiation, the core would be squeezed to higher temperatures (this was one of the original ideas for how the Sun was powered).

The Sun would continue to glow brightly for tens of millions of years before reaching the limit of its contraction, and then, as a big ball of hydrogen and helium, would cool down towards absolute zero over billions of years. 

Space colonies

How close are we to realising the dream of humankind travelling to other worlds and solar systems, perhaps even colonising them. Also, what are the most likely means of interstellar travel and humans actually surviving the many hazards it will probably involve, such as massive acceleration forces or high-velocity particles?

Travelling beyond the solar system is an old and fabulous human dream. The technological advances needed to achieve this are immense, and I suspect it will require several centuries of advances in almost every field of human endeavour before we can do this, if it is possible at all.

An important first step towards seeing whether we can actually achieve this is the exploration and settlement of our immediate space environment, starting in Earth orbit and moving on to the Moon, and Mars. It will be on Mars, the most hospitable world in our solar systems for human life, that we can answer the question as to whether or not humanity can become a multi-planet species, or whether we must be content with living on Earth. We don't know if it will be possible to live off our planet, but I believe it is important that we try.

Acceleration is not a problem as it can be done gradually. I'm told that the launch of a NASA shuttle is not uncomfortable for the astronauts. Dangerous radiation, bone loss and muscle deterioration in space are the main problems. In time, all these problems will probably be overcome. Then the major problem for long-term travel will probably be psychological health.

During this century we can expect to see exploration bases established on the Moon and Mars, comparable with those already existing in Antarctica. Just possibly astronauts might venture even further afield within the Solar System. But the stars will remain unreachable.

How big can black holes grow?

In recent decades, astronomers have come to believe that supermassive black holes probably lie at the hearts of most large galaxies. Our own Milky Way galaxy, for example, is thought to contain a central black hole as massive as four million suns, and the relatively nearby supergiant elliptical galaxy M87 is thought to have a black hole of 6 billion solar masses. Other distant galaxies are thought to have even more massive central black holes. How big can black holes grow? New research from the University of Leicester in England suggests that black holes at the hearts of galaxies could grow as massive as 50 billion suns before losing the disks of gas they need to sustain themselves. The paper – titled How Big Can a Black Hole Grow? – is published in the journal Monthly Notices Letters of the Royal Astronomical Society.
Astronomical theorist Andrew King led the research, which explores the regions of space around supermassive black holes, where the gas that feeds the hole settles into an orbiting disk. According to a December 18, 2015 statement from the University of Leicester:

This gas can lose energy and fall inwards, feeding the black hole. But these discs are known to be unstable and prone to crumbling into stars.

Professor King calculated how big a black hole would have to be for its outer edge to keep a disc from forming, coming up with the figure of 50 billion solar masses.

The study suggests that without a disc, the black hole would stop growing, meaning 50 billion suns would roughly be the upper limit. The only way it could get larger is if a star happened to fall straight in or another black hole merged with it.




Professor King added:

The significance of this discovery is that astronomers have found black holes of almost the maximum mass, by observing the huge amount of radiation given off by the gas disc as it falls in. The mass limit means that this procedure should not turn up any masses much bigger than those we know, because there would not be a luminous disc.

Bigger black hole masses are in principle possible – for example, a hole near the maximum mass could merge with another black hole, and the result would be bigger still. But no light would be produced in this merger, and the bigger merged black hole could not have a disc of gas that would make light.

One might nevertheless detect it in other ways, for example as it bent light rays passing very close to it (gravitational lensing) or perhaps in future from the gravitational waves that Einstein’s General Theory of Relativity predicts would be emitted as it merged.

Wonderful Falcon 9 landing in Florida (video)

10 surprises about our solar system

A collection of 10 unexpected and intriguing facts about our solar system – our sun and its family of planets – you probably did not know!

1. The hottest planet isn’t closest to the sun. Many people know that Mercury is the closest planet to the sun, well less than half of the Earth’s distance. It is no mystery, therefore, why people would assume that Mercury is the hottest planet. We know that Venus, the second planet away from the sun, is on the average 30 million miles farther from the sun than Mercury. The natural assumption is that being farther away, it must be cooler. But assumptions can be dangerous. For practical consideration, Mercury has no atmosphere, no warming blanket to help it maintain the sun’s heat. Venus, on the other hand, is shrouded by an unexpectedly thick atmosphere, about 100 times thicker than our own on Earth. This in itself would normally serve to prevent some of the sun’s energy from escaping back into space and thus raise the overall temperature of the planet. But in addition to the atmosphere’s thickness, it is composed almost entirely of carbon dioxide, a potent greenhouse gas. The carbon dioxide freely lets solar energy in, but is far less transparent to the longer wavelength radiation emitted by the heated surface. Thus the temperature rises to a level far above what would be expected, making it the hottest planet. In fact the average temperature on Venus is about 875 degrees F, hot enough to melt tin and lead. The maximum temperature on Mercury, the planet closer to the sun, is about 800 degrees F. In addition, the lack of atmosphere causes Mercury’s surface temperature to vary by hundreds of degrees, whereas the thick mantle of carbon dioxide keeps the surface temperature of Venus steady, hardly varying at all, anywhere on the planet or any time of day or night!

2. Pluto is smaller than the USA. The greatest distance across the contiguous United States is nearly 2,900 miles (from Northern California to Maine). By the best current estimates, Pluto is just over 1400 miles across, less than half the width of the U.S. Certainly in size it is much smaller than any major planet, perhaps making it a bit easier to understand why a few years ago it was “demoted” from full planet status. It is now known as a “dwarf planet.”

3. George Lucas doesn’t know much about “asteroid fields.” In many science fiction movies, spacecraft are often endangered by pesky asteroid fields. In actuality, the only asteroid belt we are aware of exists between Mars and Jupiter, and although there are tens of thousands of asteroids in it (perhaps more), they are quite widely spaced and the likelihood of colliding with one is small. In fact, spacecraft must be deliberately and carefully guided to asteroids to have a chance of even photographing one. Given the presumed manner of creation, it is highly unlikely that spacefarers will ever encounter asteroid swarms or fields in deep space.

4. You can make volcanos using water as magma. Mention volcanoes and everyone immediately thinks of Mount St. Helens, Mount Vesuvius, or maybe the lava caldera of Mauna Loa in Hawaii. Volcanos require molten rock called lava (or “magma” when still underground), right? Not really. A volcano forms when an underground reservoir of a hot, fluid mineral or gas erupts onto the surface of a planet or other non-stellar astronomical body. The exact composition of the mineral can vary greatly. On Earth, most volcanoes sport lava (or magma) that has silicon, iron, magnesium, sodium, and a host of complicated minerals. The volcanoes of Jupiter’s moon Io appear to be composed mostly of sulfur and sulfur dioxide. But it can be simpler than that. On Saturn’s moon Enceladus, Neptune’s moon Triton, and others, the driving force is ice, good old frozen H20! Water expands when it freezes and enormous pressures can build up, just as in a “normal” volcano on Earth. When the ice erupts, a “cryovolcano” is formed. So volcanoes can operate on water as well as molten rock. By the way, we have relatively small scale eruptions of water on Earth called geysers. They are associated with superheated water that has come into contact with a hot reservoir of magma.

5. The edge of the solar system is 1,000 times farther away than Pluto. You might still think of the solar system as extending out to the orbit of the much-loved dwarf planet Pluto. Today we don’t even consider Pluto a full-fledged planet, but the impression remains. Still, we have discovered numerous objects orbiting the sun that are considerably farther than Pluto. These are “Trans-Neptunian Objects” (TNOs), or “Kuiper Belt Objects” (KBOs). The Kuiper Belt, the first of the sun’s two reservoirs of cometary material, is thought to extend to 50 or 60 astronomical units (AU, or the average distance of the Earth from the sun). An even farther part of the solar system, the huge but tenuous Oort comet cloud, may extend to 50,000 AU from the sun, or about half a light year – more than a thousand times farther than Pluto.

6. Almost everything on Earth is a rare element. The elemental composition of planet Earth is mostly iron, oxygen, silicon, magnesium, sulfur, nickel, calcium, sodium, and aluminum. While such elements have been detected in locations throughout the universe, they are merely trace elements, vastly overshadowed by the much greater abundances of hydrogen and helium. Thus Earth, for the most part, is composed of rare elements. This does not signify any special place for Earth, however. The cloud from which the Earth formed had a much higher abundance of hydrogen and helium, but being light gases, they were driven away into space by the sun’s heat as the Earth formed.

7. There are Mars rocks on Earth (and we didn’t bring here). Chemical analysis of meteorites found in Antarctica, the Sahara Desert, and elsewhere have been shown by various means to have originated on Mars. For example, some contain pockets of gas that is chemically identical to the martian atmosphere. These meteorites may have been blasted away from Mars due to a larger meteoroid or asteroid impact on Mars, or by a huge volcanic eruption, and later collided with Earth.

8. Jupiter has the biggest ocean of any planet. Orbiting in cold space five times farther from the sun than Earth, Jupiter retained much higher levels of hydrogen and helium when it formed than did our planet. In fact, Jupiter is mostly hydrogen and helium. Given the planet’s mass and chemical composition, physics demands that way down under the cold cloud tops, pressures rise to the point that the hydrogen must turn to liquid. In fact there should be a deep planetary ocean of liquid hydrogen. Computer models show that not only is this the largest ocean known in the solar system, but that it is about 40,000 km deep – roughly as deep as the Earth is around!

9. Even really small bodies can have moons. It was once thought that only objects as large as planets could have natural satellites or moons. In fact the existence of moons, or the capability of a planet to gravitationally control a moon in orbit, was sometimes used as part of the definition of what a planet truly is. It just didn’t seem reasonable that smaller celestial bodies had enough gravity to hold a moon. After all, Mercury and Venus have none at all, and Mars has only tiny moons. But in 1993, the Galileo probe passed the 20-mile wide asteroid Ida and discovered its one-mile wide moon, Dactyl. Since then moons have been discovered orbiting nearly 200 other minor planets, further complicating the definition of a “true” planet.

10. We live inside the sun. Normally we think of the sun as being that big, hot ball of light 93 million miles away. But actually, the sun’s outer atmosphere extends far beyond its visible surface. Our planet orbits within this tenuous atmosphere, and we see evidence of this when gusts of the solar wind generate the Northern and Southern Lights. In that sense, we definitely live “inside” the sun. But the solar atmosphere doesn’t end at Earth. Auroras have been observed on Jupiter, Saturn, Uranus, and even distant Neptune. In fact, the outer solar atmosphere, called the “heliosphere,” is thought to extend at least 100 A.U. That’s nearly 10 billion miles. In fact the atmosphere is likely teardrop shaped due to the sun’s motion in space, with the “tail” extending tens to hundreds of billions of miles downwind.

What we know?

What do we know about this world?

















































































Maybe we dont know nothing ! It easy beacause we dont know how much we know about the world !!!

Happy new year 2015 !!!

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Amazing facts about space !

1. Neutron stars can spin at a rate of 600 rotations per second.

Neutron stars are one of the possible evolutionary end-points of high mass stars. They're born in a core-collapse supernova star explosion and subsequently rotate extremely rapidly as a consequence of their physics. Neutron stars can rotate up to 60 times per second after born. Under special circumstances, this rate can increase to more than 600 times per second.

2. All of space is completely silent.

Sound waves need a medium to travel through. Since there is no atmosphere in space, space will always be eerily silent.

You may be asking how astronauts can talk to each other in space. Lucky for them, radio waves can travel through space. No problem there, Houston.

3. There is an uncountable number of stars in the known universe.

We basically have no idea how many stars there are in the universe. Right now we use our estimate of how many stars there are in our own galaxy, the Milky Way. We then multiply that number by the best guesstimate of the number of galaxies in the universe. After all that math, NASA can only confidently say that say there all zillions of uncountable stars. A zillion is any uncountable amount.

An Australian National University study put their estimate at 70 sextillion. Put another way, that's 70,000 million million million. This figure is basically a guess, though.

4. The Apollo astronauts' footprints on the moon will probably stay there for at least 100 million years.

Since the moon doesn't have an atmosphere, there's no wind or water to erode or wash away the Apollo astronauts' mark on the moon. That means their footprints, roverprints, spaceship prints, and discarded materials will stay preserved on the moon for a very long time.

They won't stay on there forever, though. The moon still a dynamic environment. It's actually being constantly bombarded with "micrometeorites," which means that erosion is still happening on the moon, just very slowly.

5. 99% of our solar system's mass is the sun.

Our star, the Sun, is so dense that it accounts for a whopping 99% of our entire solar system. That's what it allows it to dominate it gravitationally. Technically, our Sun is a "G-type main-sequence star" which means that every second, it fuses approximately 600 million tons of hydrogen to helium. This means that it also converts about 4 million tons of matter to energy as a byproduct.

Being the type of star that the Sun is, it also means that when it dies, it will become a red giant and envelop the earth and everything on it. But don't worry: That won't happen for another 5 billion years.

6. More energy from the sun hits Earth every hour than the planet uses in a year.

You should be sad to know that solar technology produces less than one-tenth of 1% of global energy demand. This is due to several factors, including how much land is required for solar panels to capture enough energy for a population of people to use, how unreliable it is in bad weather and at night, and how expensive the technology is to install.

Despite all these drawbacks, the use of solar energy has increased at a rate of 20% each year for the past 15 years.

7. If two pieces of the same type of metal touch in space, they will bond and be permanently stuck together.

This amazing effect is called cold welding. It happens because the atoms of the individual pieces of metal have no way of knowing that they are different pieces of metal, so the lumps join together. This wouldn't happen on earth because there is air and water separating the pieces. The effect has a lot of implication for spacecraft construction and the future of metal-based construction in vacuums.

8. The largest asteroid ever recorded is a mammoth piece of space rock named Ceres.

The asteroid is almost 600 miles in diameter. It's by far the largest in the asteroid belt and accounts for a whole third of the belt's mass. The surface area is approximately equal to the land area of India or Argentina. It's so big, there's actually some debate over whether to refer to it as a dwarf planet instead of an asteroid, even if it has mostly asteroid-like qualities.

Ceres piques our interest specifically, as water in the form of ice has been spotted on its surface. An unmanned spacecraft named Dawn is due to be orbiting the space rock by 2015.