So when a detector in New Mexico began registering streams of charged particles coming from the general direction of the Orion nebula and about 500 light-years from Earth — a neighbor by astronomical measures — scientists took note.

“I can’t tell you what it is, but I can tell you what it isn’t,” said University of Maryland physicist Jordan Goodman, “It isn’t a statistical fluctuation in our data. It’s not an error.”

Scientists aren’t sure what causes cosmic rays, which are charged particles, namely protons and electrons, moving at high speeds due to unknown events. The list of candidates includes supernova explosions and quasars.

Uranus , the seventh planet from the Sun, is the third largest and fourth most massive planet in the solar system. It is named after the ancient Greek deity of the sky (Uranus), the father of Kronos (Saturn) and grandfather of Zeus (Jupiter). Uranus was the first planet discovered in modern times.

Characteristics of black holes

The gravitational force is strong near a black hole because all the black hole’s matter is concentrated at a single point in its center. Physicists call this point a singularity. It is believed to be much smaller than an atom’s nucleus.

The surface of a black hole is known as the event horizon. This is not a normal surface that you could see or touch. At the event horizon, the pull of gravity becomes infinitely strong. Thus, an object can exist there for only an instant as it plunges inward at the speed of light.

Astronomers use the radius of the event horizon to specify the size of a black hole. The radius of a black hole measured in kilometers equals three times the number of solar masses of material in the black hole. One solar mass is the mass (amount of matter) of the sun.

No one has yet discovered a black hole for certain. To prove that a compact object is a black hole, scientists would have to measure effects that only a black hole could produce. Two such effects would be a severe bending of a light beam and an extreme slowing of time. But astronomers have found compact objects that are almost certainly black holes. The astronomers refer to these objects simply as “black holes” in spite of the small amount of uncertainty. The remainder of this article follows that practice.

Formation of black holes

According to general relativity, a black hole can form when a massive star runs out of nuclear fuel and is crushed by its own gravitational force. While a star burns fuel, it creates an outward push that counters the inward pull of gravity. When no fuel remains, the star can no longer support its own weight. As a result, the core of the star collapses. If the mass of the core is three or more solar masses, the core collapses into a singularity in a fraction of a second.

Galactic black holes

Most astronomers believe that the Milky Way Galaxy — the galaxy in which our solar system is located — contains millions of black holes. Scientists have found a number of black holes in the Milky Way. These objects are in binary stars that give off X rays. A binary star is a pair of stars that orbit each other.

In a binary system containing a black hole, that object and a normal, visible star orbit one another closely. As a result, the black hole strips gas from the normal star, and the gas falls violently toward the black hole. Friction between the gas atoms heats the gas near the event horizon to several million degrees. Consequently, energy radiates from the gas as X rays. Astronomers have detected this radiation with X-ray telescopes.

Astronomers believe that a number of binary star systems contain black holes for two reasons: (1) Each system is a source of intense and variable X rays. The existence of these rays proves that the system contains a compact star — either a black hole or a less compact object called a neutron star. (2) The visible star orbits the compact object at such a high velocity that the object must be more massive than three solar masses.

Supermassive black holes

Scientists believe that most galaxies have a supermassive black hole at the center. The mass of each of those objects is thought to be between 1 million and 1 billion solar masses. Astronomers suspect that supermassive black holes formed several billion years ago from gas that accumulated in the centers of the galaxies.

There is strong evidence that a supermassive black hole lies at the center of the Milky Way. Astronomers believe this black hole is a radio-wave source known as Sagittarius A* (SgrA*). The clearest indication that SgrA* is a supermassive black hole is the rapid movement of stars around it. The fastest of these stars appears to orbit SgrA* every 15.2 years at speeds that reach about 3,100 miles (5,000 kilometers) per second. The star’s motion has led astronomers to conclude that an object several million times as massive as the sun must lie inside the star’s orbit. The only known object that could be that massive and fit inside the star’s orbit is a black hole.

Oort assumed that stars passing through the cloud would cause a fresh batch of comets to fall in towards the sun, where they become visible to astronomers. Such a disturbance could have long-term effects.

“The comets we see now could be from a stellar passage hundreds of millions of years ago,” said Hans Rickman of the Uppsala Astronomical Observatory in Sweden.

However, Rickman and his colleagues have confirmed that star encounters alone cannot explain comet behavior. Using a computer model of the Oort cloud, they show that gravity effects from the galaxy are equally important. The results are reported in a recent article in the journal Celestial Mechanics and Dynamical Astronomy.

Two stars passing in the night

Although Earth has almost certainly been hit by comets throughout its history, it is not all that clear how often that has happened. Much of the crater history on Earth has been erased because of erosion or tectonic activity. The remaining craters could have come from asteroids instead of comets.

“It’s quite difficult to tell a comet-induced crater from an asteroid one, since the impactor gets essentially vaporized,” Rickman said.

Comet impacts are, however, likely to be more energetic (and therefore more damaging), since comets are moving much faster than asteroids when they pass by Earth.

Comet orbits can be altered whenever another star comes within 10,000 AU of our sun. Such a close encounter — occurring every 100 million years or so — will not typically disturb asteroids or planets, but it definitely “shakes up the whole Oort cloud,” Rickman said.

Most scientists have presumed that these star crossings will lead to a shower of comets raining down on the Earth and the rest of the inner solar system. Some have even claimed to find evidence of periodic mass extinctions that might be explained by a single (as-yet-unidentified) star in an elliptical orbit around the sun.

To study the effect of stellar perturbations, Rickman and his colleagues model the Oort cloud with a sample of one million comets (the true number of cloud comets is unknown, but certainly much higher). The simulations are allowed to run for a time period corresponding to the 5-billion-year age of the solar system.

The results show that stars can induce comet showers, but the contrast with non-shower periods is less than what people have thought before, Rickman said. This leveling out in comet activity is due to the influence of the gravitational field of the Milky Way.

Veteran space flyer and aquanaut Nicholas Patrick lead the undersea mission aboard the National Oceanic and Atmospheric Administration (NOAA) Aquarius Underwater Laboratory. NASA Astronaut Richard Arnold, Japan Aerospace Exploration Agency (JAXA) Astronaut Satoshi Furukawa and systems integration engineer Christopher Gerty completed the crew.

During the NASA Extreme Environment Mission Operations 13 (NEEMO 13), the crew conducted a variety of undersea “moon walks” to test concepts for future lunar exploration using advanced navigation and communication equipment.

“This crew will work much more independently from the mission control team than on previous missions,” said NEEMO Project Manager Bill Todd of the United Space Alliance at NASA’s Johnson Space Center in Houston. “This autonomous mode of operation will encourage the crew to make real-time decisions about daily operations similar to what we think will be necessary for lunar and Mars missions. The idea is to show how procedures and training for future missions can be adapted, considering the reduced direct communication with Mission Control those crews will encounter.”

At roughly 1:50 a.m. ET on October 7, MESSENGER’s most recent images began to be received back on Earth. The spectacular image shown here is one of the first to be returned. It shows Mercury about 90 minutes after the spacecraft’s closest approach. The bright crater just south of the center of the image is Kuiper, identified on images from the Mariner 10 mission in the 1970s. For most of the terrain east of Kuiper, toward the limb (edge) of the planet, the departing images are the first spacecraft views of that portion of Mercury’s surface. A striking characteristic of this newly imaged area is the large pattern of rays that extend from the northern region of Mercury to regions south of Kuiper.

“It’s so simple,” says Ermanno F. Borra, physics professor at the Optics Laboratory of Laval University in Quebec, Canada. “Isaac Newton knew that any liquid, if put into a shallow container and set spinning, naturally assumes a parabolic shape—the same shape needed by a telescope mirror to bring starlight to a focus. This could be the key to making a giant lunar observatory.”

Borra, who has been studying liquid-mirror telescopes since 1992, and Simon P. “Pete” Worden, now director of NASA Ames Research Center, are members of a team taking the idea for a spin.

On Earth, a liquid mirror can be made quite smooth and perfect if it its container is kept exactly horizontal and rests on a low-vibration low-friction air bearing that is spun by a synchronous motor having one stable speed. “It doesn’t need to spin very fast,” says Borra. “The rim of a 4-meter–diameter mirror—the largest I’ve made in my lab—travels only 3 miles per hour, about the speed of a brisk walk. In the low gravity of the Moon, it would spin even slower.”

Most liquid-mirror telescopes on Earth have used mercury. Mercury remains molten at room temperature, and it reflects about 75 percent of incoming light, almost as good as silver. The biggest liquid-mirror telescope on Earth, the Large Zenith Telescope operated by the University of British Columbia in Canada, is 6 meters across—a diameter 20 percent larger than the famous 200-inch mirror of the Hale telescope at Palomar Observatory in California. Yet when completed in 2005, the Canadian Palomar-class liquid-mirror telescope cost less than $1 million to build—only a few percent the cost of a solid-mirror telescope of the same diameter–and, for that matter, only a sixth of Palomar’s original cost in 1948.

Those economics are making astronomers sit up and begin noodling out plans for a lunar observatory.

“Our study started when I was still an astronomy professor at the University of Arizona before I came to NASA in 2006,” Worden recalls. “The real appeal of this approach is that we could get an unbelievably large telescope on the Moon.”

Some astronauts have complained about being in zero G because it makes their work difficult. Objects like screwdrivers and screws don’t stay still but float around. You can’t use your body’s weight to hold things down – you have to brace yourself against something rigid, and so on. It would be easier to do their experiments on the ground.

Neptune is the eighth and farthest known planet from the Sun in the Solar System. It is the fourth largest planet by diameter, and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 14 Earth masses and less dense. The planet is named after the Roman god of the sea. Its astronomical symbol is Astronomical symbol for Neptune., a stylized version of Poseidon’s Trident.

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Along with the planets Jupiter, Uranus, and Neptune, it is classified as a gas giant (also known as a Jovian planet, after the planet Jupiter). It was named after the Roman god Saturnus, equated to the Greek Kronos (the Titan father of Zeus) and the Babylonian Ninurta. Saturn’s symbol represents the god’s sickle . The day in the week Saturday gets its name from the planet.