Mission to Mars (16 page)

An Arizona crater: remains of an asteroid impact

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Illustration Credit 5.4
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Siberian forest in ruins: aftermath of a 1908 asteroid

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Illustration Credit 5.5
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Take note that some 75 percent of Earth is covered by water. What are the consequences if a medium-size asteroid plowed into deep ocean waters?

Research carried out by the late Elisabetta Pierazzo, a senior scientist at the Planetary Science Institute in Tucson, Arizona, served up some bad news. Her work indicated that an asteroid crashing into the deep ocean could have dramatic worldwide environmental effects, including depletion of Earth’s protective ozone layer for several years.

There has long been interest in the effects of oceanic impacts of medium-size asteroids, but more focused on the danger of stirring up a regional tsunami. But Pierazzo’s approach used computer-modeling scenarios to look at the effects such a strike would have on the atmospheric ozone. The results suggest that midlatitude oceanic impacts of one-kilometer asteroids can produce major global perturbation of upper atmospheric chemistry, including multiyear global ozone lessening.

Pierazzo found that rapidly ejected seawater from an NEO strike includes water vapor and compounds like chloride and bromide that hasten the destruction of the ozone, all of which would influence atmospheric chemistry. Indeed, the removal of a significant amount of ozone in the upper atmosphere for an
extended period of time, she found, would have important biological repercussions at Earth’s surface—such as an increase in ultraviolet rays that reach terra firma.

So be it by land, air, or sea, getting to know NEOs, I believe, is high on the space program’s to-do list. The overall message in terms of planetary defense is that there’s need to find them before they find us.

By making use of ground- and space-based technology, humankind does have the ability to anticipate a large-scale impact. Preventing such an occurrence is another matter. Still, to protect life from such a vicious event is an environmental challenge, one that calls upon integrating technology, space policy, and international involvement to launch a global response.

Several fellow space travelers have maintained a long-standing interest in NEOs.

A leader in taking on the NEO challenge is Rusty Schweickart, Apollo 9 astronaut and chairman emeritus of the B612 Foundation. That group announced last year their aim to fund-raise, build, launch, and operate the world’s first privately funded deep space telescope mission. Called Sentinel, this project would identify the current and future locations and trajectories of Earth-crossing asteroids. The mission calls for a space telescope—to be built by Ball Aerospace in Boulder, Colorado—to be placed in orbit around the sun, ranging up to 170 million miles from Earth, for a mission of discovery and mapping.

Sentinel appears to be technically sound and on track for a 2017 launch to protect Earth by providing early warning of threatening asteroids. B612 and Ball Aerospace have developed a very viable detection method for finding and tracking
near-Earth asteroids. In addition, NASA has forged a Space Act Agreement with the B612 organization to pursue innovative in-space survey skills for detection of new NEO targets.

“For the first time in history, B612’s Sentinel mission will create a comprehensive and dynamic map of the inner solar system in which we live—providing vital information about who we are, who are our neighbors, and where we are going,” reports Schweickart. “We will know which asteroids will pass close to Earth and when, and which if any of these asteroids actually threaten to collide with Earth. The nice thing about asteroids is that once you’ve found them and once you have a good solid orbit on them you can predict a hundred years ahead of time whether there is a likelihood of an impact with Earth.”

Astronaut Ed Lu, veteran of space shuttle, Soyuz, and space station missions, is the B612 Foundation chairman and CEO. The extraordinary B612 Sentinel mission extends the emerging commercial spaceflight industry into deep space—a first that will pave the way for many other ventures. “Mapping the presence of thousands of near-Earth objects will create a new scientific database and greatly enhance our stewardship of the planet,” Lu believes.

Robotic spacecraft surveys a large asteroid
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Illustration Credit 5.6
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Private Sentinel telescope eyes asteroid population
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Illustration Credit 5.7
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Along with the need to come to terms with the dangers of asteroids, there are several other important outcomes of their study. The United States, Europe, and Japan have successfully hurled spacecraft to asteroids, with more robotic probes to key NEOs on the books.

Russian engineers have been promoting the idea of an automated craft emplacing a location transmitter on asteroid 99942 Apophis, to maintain a more accurate track of this potentially
hazardous 690-to-1,080-foot-diameter object. By doing that, we would obtain a very accurate orbit of this NEO, along with an early warning of whether it’s on a menacing course with Earth in the years to come.

We already know that the Apophis trajectory places it on an extremely close flyby of Earth in 2029—it is so close, in fact, that it will zip below our geosynchronous satellites. Earth’s gravitational tug on Apophis, some worry, may alter its course in such a way as to run into our planet in 2036. But the chance of that happening, experts say, is very, very slim.

My review of Apophis has been enlightening in several ways, specifically in picturing a rotating Earth orbit around the sun where the sun-Earth line is fixed. What an NEO does, if its semi-major axis is
inside
Earth: It does a series of loops around the inside of that circle, then comes back within the vicinity of Earth. Those set of loops are essentially the number of years before it comes back close to Earth.

By Apophis whisking past Earth in 2029, that gravity-assist pass is going to change this NEO so its semi-major axis is
outside
Earth. Until 2036, it will do a series of loops that are outside the circle and traveling in the opposite direction. In other words, Earth’s rotating coordinate frame is moving ahead of Apophis.

Simply, Apophis is going to be doing loop-the-loops, getting ahead of Earth, and then it’s going to buzz by Earth and do loop-the-loops outside of Earth’s orbit. That’s what the gravity swingby of planet Earth is doing to this NEO, and I was really amazed when I found that out.

It is a good lesson learned on what an asteroid and its orbit around the sun, or period, do in terms of its availability for a
revisit by a robot or a human crew, which is not a constant. It is analogous to understanding some of the inertial cycler orbits that are necessary to sustain a long-term space program.

Visitation of NEOs by robotic craft certainly paves the way for human exploration of specific asteroids in the future.

In understanding and coping with the hazard of devastating impacts by NEOs on Earth, we can learn about the physical nature of NEOs. Doing that, in turn, can incrementally enhance our odds of effectively dealing with an NEO, should one of these objects be discovered that could gravely affect us. Furthermore, melding human and robotic abilities at an NEO serves as a test bed to perfect our skills for working at ever greater distances.

In my estimation, human visits to NEOs can go partway toward appreciating the challenges of travel to Mars, without invoking the most severe difficulties. Mars must remain a decisive destination, but NEOs offer a special, practical, and inspiring challenge that gives us the “space legs” to propel deeper toward the red planet.

My research colleague Anthony Genova, at the NASA Ames Research Center, is of like mind. Human exploration of NEOs offers valuable and exciting opportunities as stepping-stones to eventual Mars exploration and colonization. He, too, supports a stepping-stone approach—similar to that seen in the Apollo program—as NEO missions not only reduce the overall risk and complexity of a human space exploration program, but also decrease the wait time needed for the next “new” mission, allowing the public to lend its crucial support to the program much earlier than would otherwise be anticipated without intermediate exploration achievements.

NASA scientists simulate an asteroid rendezvous
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Illustration Credit 5.8
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Although asteroids routinely zoom by close to Earth, even within the moon’s orbit, larger and more interesting asteroids may be tens of millions of miles away. That’s a lengthy haul for people without a resupply of water, food, or air—a mission longer than has ever been attempted in space and far different from the cargo craft that routinely visit the International Space Station.

NASA’s current goal of having astronauts on an asteroid-bound mission by 2025 is a core idea promoted by U.S. President
Obama. That call represented a major shift from the space agency’s earlier plan, which was aimed at replanting U.S. astronauts on the moon.

Since Obama’s 2010 space speech, the interest in transporting astronauts to an asteroid has picked up speed, not only at NASA but also within the aerospace community. The rationale is that such a deep space expedition not only tests out hardware but also builds confidence in humans performing long-duration journeys to other destinations, like the moons of Mars, or onward to the red planet itself. At the same time, a piloted journey to an NEO would provide the savvy to deal with a future space rock found to be on a collision course with Earth.

I term these asteroid explorers “NEOphytes,” and they have projected that a human trek to one of those mini-worlds may involve two or three astronauts on a 90-to-120-day spaceflight. The round-trip travel includes a week or two-week stay at the appointed asteroid.

One blueprinted NEO mission, an early human asteroid mission that uses NASA’s Orion spacecraft, has been dubbed Plymouth Rock. That plan has been scripted by Orion’s builder, Lockheed Martin, and detailed by advanced planner Josh Hopkins.