Though that number might seem random, it comes from measuring the frequency of microwaves needed to excite the cesium atoms in the average of the earlier definition of 1 second. These measurements were taken over a span of nearly three years, Scientific American reported.

Currently, hundreds of cesium atomic clocks are responsible for keeping global time and controlling GPS navigation. But in the past decade, another generation of atomic clocks has emerged, called "optical clocks," and they are 100 times more precise than the cesium variety. The new clocks work in the exact same way as the cesium ones, except they use atoms such as aluminum or ytterbium that get excited by higher frequencies of visible light (hence the name "optical") rather than the slower microwaves. This higher frequency adds more data points to the definition of a "second," making the measurement more precise. [7 Strange Facts About Quarks]

To understand this, imagine the different types of clocks as a pair of rulers, said Murray Barrett, an associate physics professor at the National University of Singapore and the lead author of the new study. If the older, "cesium" ruler measures a line that's 20 centimeters (7.9 inches) long, the more precise, "optical" ruler can measure the line also as, for example, 200 millimeters.

While optical clocks are very precise , getting them to run for a very long period of time and to remain stable in their environments can be problematic, Barrett said. A room's temperature can change the electromagnetic fields acting on the atoms, which in turn can skew the time measurement, Barrett said. So, the cesium clocks are still "much more reliable in their implementation than [the new] optical clocks," Barrett told Live Science.

Making less sensitive atomic clocks

In their new study, Barrett and his team found that a lutetium ion is less sensitive to changes in environmental temperature than are any other elements used for optical clocks, making it a strong candidate to serve as master time keeper.

Lutetium atoms can also help compensate for another problem affecting time measurement, the team found. Because the atoms used in these clocks are charged, they slightly wiggle back and forth in response to the electromagnetic fields created by the waves (visible light, microwaves, etc.) — and this can skew the time measurement. Scientists call this rapid backward and forward movement a "micromotion shift."

Because scientists must compensate for this shift, it's really difficult to develop atomic clocks with more than one ion — which would make such clocks more practical, Barrett said. But the team found that they could use a natural property in a certain type of lutetium ion to cancel out these "micromotion shifts."

However, this comes at a cost: Those atoms became more sensitive to the temperature of the room. That trade-off might limit the impact of the new finding, and the atom lutetium might not be a "real game changer," said Jérôme Lodewyck, a physicist at the Paris Observatory who was not part of the study.

But, this "high-quality work" adds another possible atomic species to the long list of timekeeper candidates that is a "wealth for metrologists" looking to compare different clocks, Lodewyck said. [What's That? Your Physics Questions Answered]

Beyond telling time

Though Barrett said lutetium "is extremely promising," he doesn't think there's a big rush to redefine the second using optical clocks, as cesium clocks do just fine at things like getting us where we need to go.

But highly precise optical clocks might allow for new applications "that would simply not be possible with our current technology," Barrett said.

For example, clocks are sensitive to where they sit in the world, because time is distorted by gravity, according to Albert Einstein's theory of general relativity. Right now, atomic clocks on Earth can't detect the miniscule time-warping that occurs due to Earth's gravity.  But if researchers could place highly precise optical clocks around the world, that setup could help researchers map out the gravitational field of our planet, Barrett said.

Further, highly precise atomic clocks could detect matter and energy we may not yet be able to see, Lodewyck said. That could include dark matter, which exerts a gravitational pull yet does not interact with ordinary light, and dark energy, the mysterious force that seems to be accelerating the expansion of the universe, he said.

Here's how it might work: If you know the frequency needed to excite some atoms in the time frame of a second, you could use these various clocks around the world to detect any differences beyond what you would normally expect. There are "some theories that say dark matter is around us, so if we cross a chunk of dark matter, this would perturb the clock," Lodewyck told Live Science.

There may even be applications we can't think of right now, Barrett said. "Certainly, when we first started developing clocks for the purpose of ship navigation, we never imagined the idea of somebody being able to walk around and know exactly where they are in a big city."

• Originally published on Live Science.

Vesta is the second most massive body in the asteroid belt, surpassed only by Ceres, which is classified as a dwarf planet. The brightest asteroid in the sky, Vesta is occasionally visible from Earth with the naked eye. It is the first asteroid to be visited by a spacecraft. The Dawn mission orbited Vesta in 2011, providing new insights into this rocky world.

Celestial Police

In 1596, while determining the elliptical shape of planetary orbits, Johannes Kepler came to believe that a planet should exist in the gap between Mars and Jupiter. Mathematical calculations by Johann Daniel Titius and Johann Elert Bode in 1772 — later known as the Titius-Bode law — seemed to support this prediction. In August 1798, a group known as the Celestial Police formed to search for this missing planet. Among these was German astronomer Heinrich Olbers. Olbers discovered the second known asteroid, Pallas. In a letter to a fellow astronomer, he put forth the first theory of asteroid origin. He wrote, "Could it be that Ceres and Pallas are just a pair of fragments … of a once greater planet which at one time occupied its proper place between Mars and Jupiter?"

Olbers reasoned that the fragments of such a planet would intersect at the point of the explosion, and again in the orbit directly opposite. He observed these two areas nightly, and on March 29, 1807, discovered Vesta, becoming the first person to discover two asteroids. After measuring several nights' worth of observations, Olbers sent his calculations to mathematician Carl Friedrich Gauss, who remarkably computed the orbit of Pallas in only 10 hours. As such, he was given the honor of naming the new body. He chose the name Vesta, goddess of the hearth, and sister to Ceres. [Photos: Asteroid Vesta and NASA's Dawn Spacecraft]

Physical characteristics of Vesta

Vesta is unique among asteroids in that it has light and dark patches on the surface, much like the moon. Ground-based observations determined that the asteroid has basaltic regions, meaning that lava once flowed across its surface. It has an irregular shape, roughly that of an oblate spheroid (in nontechnical terms, a somewhat smooshed sphere). 

• Diameter: 329 miles (530 kilometers)
• Mass: 5.886 X 10²⁰ lbs. (2.67 x 10²⁰ kilograms)
• Temperature: 85 to 255 K (minus 306 to 0 degrees Fahrenheit / minus 188 to minus 18 degrees Celsius)
• Albedo: 0.4322
• Rotation period: 5.342 hours
• Orbital period: 3.63 years
• Eccentricity: .0886
• Aphelion: 2.57 AU
• Perihelion: 2.15 AU
• Closest approach to Earth: 1.14 AU

Surface, composition and formation

When Vesta made a close approach to Earth in 1996, the Hubble Space Telescope mapped its topographic surface and features. This revealed a large crater at the south pole that slices into its interior. The crater averages 460 km in diameter — remember: Vesta itself is only 530 km across. It cuts an average of 13 km into the crust, and most likely formed from an impact in the asteroid's early life. The material ejected from this collision resulted in a number of smaller — Vestoid — asteroids that orbit near their parent, as well as some of the meteorites that have crashed into Earth.

Unlike most asteroids, the interior of Vesta is differentiated. Like the terrestrial planets, the asteroid has a crust of cooled lava covering a rocky mantle and an iron and nickel core. This lends credence to the argument for naming Vesta as a protoplanet, rather than as an asteroid.

Vesta's core accreted rapidly within the first 10 million years after the formation of the solar system. The basaltic crust of Vesta also formed quickly, over the course of a few million years. Volcanic eruptions on the surface stemmed from the mantle, lasting anywhere from 8 to 60 hours. The lava flows themselves ranged from a few hundred meters to several kilometers, with a thickness between 5 to 20 meters. The lava itself cooled rapidly, only to be buried again by more lava until the crust was complete. Dawn's gravity put its core at about 18 percent of Vesta's mass, or proportionally about two-thirds as massive as Earth's core.

In fact, if it weren't for Jupiter, Vesta could have had a good chance at becoming a planet.

"In the asteroid belt, Jupiter basically stirred things up so much that they weren't able to easily accrete with one another," Dawn scientist David O'Brien, of the Planetary Science Institute in Tucson, Arizona, told reporters in 2012.

"The velocities in the asteroid belt were really high, and the higher the velocity is, the harder it is for things to merge together under their own gravity," O'Brien added.

In 1960, a fireball streaking through the sky over Millbillillie, Australia, announced the arrival of a piece of Vesta on Earth. Composed almost entirely of pyroxene, a mineral found in lava flows, the meteorite bears the same spectral signals as Vesta.

NASA's Dawn spacecraft, which visited the asteroid in 2012, discovered that the rocky body had a surprising amount of hydrogen on its surface. It also found bright, reflective regions that may have been left over from its birth.

"Our analysis finds this bright material originates from Vesta and has undergone little change since the formation of Vesta over 4 billion years ago," said Jian-Yang Li, a Dawn participating scientist at the University of Maryland, College Park, in a statement.

A massive mountain towers over Vesta's southern pole. The enormous mountain reaches up over 65,000 feet (20 kilometers) in height, making it nearly as tall as Olympus Mons, the largest mountain (and volcano) in the solar system. Olympus Mons soars about 15 miles (24 kilometers) above the surface of Mars.

"The south polar mountain is larger than the big island of Hawaii, the largest mountain on Earth, as measured from the ocean floor," Dawn principle investigator Chris Russell was reported saying at a 2011 astronomical conference. "It is almost as high as the highest mountain in the solar system, the shield volcano Olympus Mons on Mars."

Liquid water once flowed across the asteroid. Images captured by the Dawn spacecraft revealed curved gullies and fan-shaped deposits within eight different Vesta impact craters. All eight of the craters are thought to have formed within the last few hundred million years, fairly recent in the lifetime of the 4.5-billion-year-old asteroid.

"Nobody expected to find evidence of water on Vesta. The surface is very cold and there is no atmosphere, so any water on the surface evaporates," study lead author Jennifer Scully, a postgraduate researcher at UCLA, said in a NASA statement. "However, Vesta is proving to be a very interesting and complex planetary body."

Scully and her team thought the features were created by debris flows, as opposed to pure-water rivers or streams, sculpted the Vesta gullies. They proposed that meteorites bombarding the asteroid melted ice deposits beneath the surface, sending liquid water and small rocky particles flowing down the crater walls. Such activity suggests the presence of ice buried beneath the surface.

"If present today, the ice would be buried too deeply to be detected by any of Dawn's instruments," Scully said. "However, the craters with curved gullies are associated with pitted terrain, which has been independently suggested as evidence for loss of volatile gases from Vesta."

Ice could have been responsible for modifying Vesta's surface. In 2017, a study suggested that smooth patches of terrain on the asteroid frequently possessed high concentrations of hydrogen, which is often seen when solar radiation breaks down water molecules.

"We suggest that modifications of the surface by melting of buried ice could be responsible for smoothing those areas," Essam Heggy, a planetary scientist at the University of Southern California in Los Angeles, told Space.com. "Buried ice could have been brought to the surface after an impact, which caused heated ice to melt and travel up through the fractures to the surface."

Dawn also observed signs of hydrated minerals (minerals containing water molecules) on Vesta's surface, which could also hint at the presence of buried ice. The hydrated materials were associated with older terrains, and could have been delivered by impacts of material from farther out in the solar system.

A low-altitude map of Vesta revealed a rich geology. The steep slopes found on the asteroid, combined with its high gravity, paves the way for rocks to roll downward, exposing other material. Dawn revealed a variety of mineral, including some bright and dark materials that could relate to potential buried ice.

Vestal visitors to Earth

In fact, Vesta's unique composition means that it is responsible for an entire group of meteorites. The HED meteorites — made up of howardites, eucrites and diogenites — tell the story of Vesta's early life. Eucrites form from hardened lava, while diogenites come from beneath the surface. Howardites are a combination of the two, formed when a large impact mixed the two sections together. 

Vesta has been suspected as being the source of the HED meteorites since 1970. Dawn's mapping spectrometer verified that proposition. The Dawn team thinks the HEDs came from an impact basin named Rheasilvia, after an ancient Roman vestal virgin priestess. At 310 miles (500 kilometers) in diameter, Rheasilvia is nearly as large as Vesta itself. It most likely formed from a collision that stripped away most of the southern hemisphere's crust, revealing the asteroid's interior.

"Vesta likely came close to shattering," said Dawn principal investigator Carol Raymond, noting that the blow left concentric sets of troughs — fracture lines — around Vesta's equator.

Parallel troughs may be another sign of the enormous impact. Raymond told the Planetary Society that the presence of those troughs suggests serious damage to the asteroid's interior.

If the orbit of Vesta lies beyond Mars, how did pieces of it manage to arrive on Earth? The fragments of Vesta pass Jupiter once every three orbits around the sun, allowing the gravity of the largest planet to affect them. Such tugging could have shifted the fragments enough to cause their eventual impact with Earth.

As a result, Vesta is one of three bodies from which scientists have samples. The other two are the moon and Mars.

Exploring the asteroid

In September 2007, NASA launched the Dawn mission, which is unique in that it was the first craft to enter orbit around one solar system body, then proceed to a second. Dawn entered orbit around Vesta in July 2011. After studying the asteroid for a year, it left Vesta encountered Ceres in March 2015. 

NASA's Dawn mission is to study the characteristics of the early solar system by analyzing the two asteroids, which are very different. Ceres is wet, with seasonal polar caps, and may have a thin atmosphere. Vesta, on the other hand, is dry and rocky. Studying the unique spectral signatures in its rocky crust will expand our knowledge of our own planet, as well as Mars and Mercury.

Given their size, the two are actually regarded as protoplanets, or small planets. The gravitational pull of Jupiter disrupted their formation. Without the presence of the gas giant, the two may well have continued to evolve into full-size planets.

"We now know that Vesta is the only intact, layered planetary building block surviving from the very earliest days of the solar system," Dawn deputy principal investigator Carol Raymond, of NASA's Jet Propulsion Laboratory in Pasadena, California, told reporters in 2012.

Dawn's study of Vesta allowed for the creation of the best map to date of the asteroid.

In October 2010, the Hubble Space Telescope imaged Vesta again. The resulting data revealed that the asteroid was tilted approximately four degrees more than scientists originally thought. These findings helped NASA to place the spacecraft in the appropriate polar orbit around the asteroid. Dawn requires light from the sun in order to perform its mapping and imaging assignments.

Additional resources

• Download this PDF about the discovery of asteroids and the Dawn mission.
• Visit this blog on the JPL website for a 3D view of Vesta.
• What did Dawn learn at Vesta? via The Planetary Society

• Follow Nola Taylor Redd at @NolaTRedd, Facebook, or Google+.
• Follow us at @Spacedotcom, Facebook or Google+. 

Putin has claimed that the vehicle is capable of reaching speeds of Mach 20 — or 20 times the speed of sound — and could evade current U.S. missile defense systems. Worryingly, the vehicle can supposedly carry a nuclear warhead, according to the intelligence sources. [7 Technologies That Transformed Warfare]

Rather than generating its own power to reach hypersonic speeds, the glide vehicle catches a ride atop an intercontinental ballistic missile (ICBM). Typically, these rockets fly to space on an arcing trajectory before releasing warheads near the top of the parabola, and these warheads drop back down onto the target at hypersonic speeds under the power of gravity.

Rather than falling back to Earth, though, Avangard  reenters the atmosphere at an angle and its aerodynamic shape generates lift that lets it glide down at hypersonic speeds, says Juliano, which allows it to travel further farther and maneuver as it descends.

Hyper engineering

The vehicle appears to follow a design known as a "waverider," Juliano said. Waveriders are hypersonic aircraft that have wedge-shaped fuselages specially designed to generate lift by surfing on the shock wave generated as its own aircraft punches through the air at a high speed.

This is important at higher altitudes, where air density is low, making it difficult to generate lift with conventional wing designs. And because it doesn't need large wings, the vehicle is more streamlined, and the reduced drag allows it to maintain its speed over a much longer distance, Juliano said.

Building a vehicle that can tolerate hypersonic speeds and the temperatures they generate is no easy feat, Juliano said. But the design the Russians have opted for circumvents one of the major challenges: propulsion. [Photos: Hypersonic Jet Could Fly 10 Times the Speed of Sound]

"Designing a successful propulsion system at Mach 10 or above is extraordinarily challenging," he said. "By putting the glider on top of an ICBM, you avoid the need to design a successful hypersonic air-breathing engine."

Controlling a vehicle at such high speeds is still incredibly tricky, though.The Russians claim that Avangard is highly maneuverable, and based on computer-generated video included in Putin's address, it appears to have several flaps similar to the aerofoils used by planes to change direction.

Adjusting the aerofoils at hypersonic speeds is not a trivial task, because the shock wave can have complex interactions with the air flowing over the vehicle's surfaces, resulting in "nonlinear" behavior, Juliano said.

That means tiny adjustments can have outsize impacts, which makes it very tricky to calculate how much to move a flap or aerofoil. "It has to be precise, it has to operate quickly and it's a much harder environment to predict," he said.

Nonetheless, Juliano thinks the Russian claims are credible, as the technology has been in development for some time. The U.S. tested its own version, dubbed Hypersonic Technology Vehicle 2, in 2010 and 2011, but both flights were failures. And China also has an experimental system, code-named DF-ZF.

What is it for?

Russian efforts to develop hypersonic glide vehicles are explicitly aimed at evading U.S. missile defense systems, said Pavel Podvig, an independent analyst who specializes in Russia's nuclear arsenal. [Could the US Stop Nuclear Weapons?]

Current U.S. defenses are designed to take out conventional warheads from ICBMs on predictable ballistic trajectories while they are still in space; these defenses are not well suited to intercept weapons coming in on a high-speed glide in the atmosphere, Podvig said. And unlike traditional warheads, the vehicles will be capable of maneuvering around defenses.

But Podvig said it's not clear if the weapons really provide useful additional military capabilities. "It has been described as a weapon in search of a mission," he told Live Science. "My take is, you don't really need this kind of capability. It doesn't really change much in terms of ability to hit targets."

Podvig pointed out that the ICBM that carried the Avangard during testing, the SS-19, normally carries six conventional warheads. If the goal is to counter missile defense systems, it would be just as easy to overwhelm them with a greater number of standard warheads, he said.

But such weapons could breed dangerous uncertainty, Podvig said, because they aren't covered by arms-control treaties such as New START, which require countries to report the number, type and location of nuclear-capable weapons like ICBMs. In addition, the capabilities and potential uses of hypersonic gliders are still unclear.

"These systemscreate greater risks of miscalculation," Podvig said, "and it's not clear if we can effectively deal with those risks."

In an effort to reduce some of that uncertainty, the Pentagon is reportedly considering fielding space-based sensors to spot hypersonic weapons, according to Space News. The approach would require a costly constellation of satellites, but would be better at spotting weapons gliding in the upper atmosphere and could also see farther than land-based systems limited by the horizon.

Podvig says a properly designed system of this kind should be able to detect hypersonic weapons in flight, but it's not clear this would make it any easier to intercept such fast and maneuverable vehicles.

Originally published on Live Science.