© unknownPhoto of Apophis
Dr. Gregory L. Matloff is an associate professor of physics at New York City College of Technology (City Tech).
He is working with NASA on an idea of heating up an asteroid with the use of a solar sail (which produces a concentrated stream of sunlight) so that a jet stream could be created on the asteroid to alter its course away from Earth.
Earth is always in jeopardy of being hit by an asteroid and other space objects. Small ones - meteorites - hit Earth all of the time and still smaller ones - meteors - enter Earth's atmosphere but burn up before reaching the ground. However, larger ones still out in space - meteoroids and even larger ones called asteroids -- are of concern to astronomers because of their potential to do great harm to our planet if they should collide with us.
Some of them are of greater concern to these asteroid trackers because they travel close to Earth. They are called Near-Earth Objects (NEOs) - those meteoroids and asteroids that travel less than 120 million miles (195 million kilometers) from Earth on their orbits about the Sun.
Thus, they are traveling about 1.3 astronomical units (AU) or less from Earth. One AU is the average distance that Earth and Sun are apart, which is around 93 million miles (150 million kilometers).
According to the January 26, 2011 City University of New York (CUNY) article "City Tech Research Team Casts Light on Asteroid Deflection," the team headed by Dr. Matloff is working on analysis of what would happen if, for example, a 25-million-ton NEO, traveling at 30,000 to 40,000 miles per hour, was heading straight toward Earth and it could somehow be diverted by a concentrated beam of sunlight.
Sound impossible? It's not!
The January 25, 2011 iTWire article "Surprise! NanoSail-D solar sail does its thing!" talks about the NanoSail-D spacecraft, which recently deployed its solar sail out in space.
Such a spacecraft is being tested to help remove space junk from orbit about Earth. The NanoSail-D has a 100-square-foot (9.2-square-meter) sail -- made of a thin polymer sheet of reflective material -- that unfurls. It could be used to add extra atmospheric drag on old satellites in orbit, so that they de-orbit faster. And, thus, less junk in space.
However, such a solar sail could also be used to divert asteroids and large meteoroids from a head-on collision with Earth.
Dr. Matloff explains the problem with NEOs: "A collision with an object of this size traveling at an estimated 30,000 to 40,000 mile per hour would be catastrophic. He says two options are available: "Either destroy the object or alter its trajectory."
Matloff suggests the latter: tweak its direction so it goes harmlessly past Earth.
The City Tech article states, "Dr. Matloff, whose research includes the best means to avert such a disaster, believes that diverting such objects is the wisest course of action. In 2029 and 2036, the asteroid Apophis (named after the Egyptian god of darkness and the void), at least 1,100 feet in diameter, 90 stories tall, and weighing an estimated 25 million tons, will make two close passes by Earth at a distance of about 22,600 miles."
Check out some of the research performed by NASA on these possible-but-unlikely collision scenarios between Apophis and Earth at: "Predicting Apophis' Earth Encounters in 2029 and 2036."
Matloff states, "We don't always know this far ahead of time that they're coming, but an Apophis impact is very unlikely."
Such a collision with Apophis (officially: 99942 Apophis) would produce gigantic force that could be tens of thousands of times more powerful than an atomic bomb.
If we try to explode such an object before it gets to Earth, the radioactive debris that result from the explosion could be a danger to Earth.
Instead, Dr. Matloff suggests that such NEOs could be diverted from their trajectory by heating its surface with a solar sail.
A solar-sail probe could be positioned near to the NEO, and its solar sail would concentrate the rays of the Sun onto the object (like a magnifying glass can focus the Sun's rays on a hot summer day) in such a way that the heat generated inside the asteroid would eventually create a jet stream.
And, that jet stream would alter the direction of the asteroid, and force it onto a path around Earth, rather than straight into the planet.
Just like a rocket is powered upward off its launch pad by the force of its propellants in the opposite direction (Newton #3: equal action and reaction), such a jet stream would force the NEO onto another slightly altered course, one away from Earth.
Currently, Dr. Matloff is working with NASA with ways to deflect such NEOs. The City Tech article states, "The team theorized that a solar collector (SC), which is a two-sail solar sail configured to perform as a concentrator of sunlight, could do the trick. Constructed of sheets of reflective metal less than one-tenth the thickness of a human hair, an SC traveling alongside an NEO for a year would concentrate the sun's rays on the asteroid, burn off part of the surface, and create the jet stream."
And, right now they are working on the specifics of such a mission, such as how much sunlight is needed to produce the desired result.
Matloff explains, "A beam that penetrates too deeply would simply heat an asteroid, but a beam that penetrates just the right amount - perhaps about a tenth of a millimeter - would create a steerable jet and achieve the purpose of deflecting the asteroid."
And, "For the past year, Dr. Matloff and a team of City Tech scientists have been experimenting with red and green lasers to see how deeply they penetrate asteroidal rock, using solid and powdered (regolith) samples from the Allende meteorite that fell in Chihuahua, Mexico in 1969."
Is this unique research? Dr. Matloff says, "To my knowledge this is the first experimental measurement of the optical transmission of asteroid samples."
The article also states that the United States and Russia -- their two space agencies, NASA and Roscosmos, respectively - are studying the Apophis asteroid because of its close encounter with Earth in 2029 and 2036.
Matloff comments on this rivalry, "At present a debate is underway between American and Russian space agencies regarding Apophis. The Russians believe that we should schedule a mission to this object probably before the first bypass because Earth-produced gravitational effects during that initial pass could conceivably alter the trajectory and properties of the object. On the other hand, Americans generally believe that while an Apophis impact is very unlikely on either pass, we should conduct experiments on an asteroid that runs no risk of ever threatening our home planet."
Check out the Wikipedia webpage "99942 Apophis" for a list of articles describing Apophis and the work being done to study the possibility of Apophis hitting Earth in 2029 and 2036.
Sounds like a pretty marginal idea - it's hard to imagine an asteroid cooperating by holding perfectly still (relative to the solar sail beam)