Tag Archives: Science

ABC Asteroid XYZ

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Spacecraft NEAR Shoemaker executed a soft landing on this asteroid, Eros, in 2000.

In “Asteroids Good and Bad” we touched on NASA’s plans to detect asteroids as well as to eventually land on one and “redirect” a piece of it into orbit around the Moon.

Why the interest in these space rocks?

Asteroids have pounded Earth for billions of years, and they’re not done with their mission, as the Chelyabinsk meteor rudely reminded us over Russia in 2013. With no warning it slammed into Earth’s atmosphere and exploded 28 miles up. Even that far away the relatively small 18-meter diameter asteroid fragment’s 500 kiloton equivalent explosion injured over 1,200 surprised people going about their business below it.

So what are asteroids? They consist of rocks and minerals, and come in three varieties: chondrite (C-class) made of clay and silicate rocks; stony (S-class) made of silicate and nickel-iron rocks; and metallic (M-class) consisting of mostly nickel-iron rock. They’re irregularly shaped, usually pitted or covered with craters.

Size matters, especially if one is headed our way. Most asteroids range from thirty feet to 330 miles in diameter, and none have any atmosphere. They orbit the Sun, rotating or tumbling along. More than half-a-million are known, but millions more are out there – exactly how many is unknown – and size matters.

Most asteroids orbit our Sun between Mars and Jupiter in the main asteroid belt. Between 1 and 2 million asteroids larger than 1 kilometer in diameter may exist in the main belt, yet most are still a million or more kilometers away from their nearest sibling. Just 150 have a companion moon, a few have two moons, and some asteroids occur as a pair of relatively equal-sized bodies. Astronomers have even spotted triple asteroids tumbling along together.

Although most asteroids may remain in the main belt, Jupiter’s massive gravity flings them out across the solar system from time to time. At present, 10,003 are known to approach Earth close enough to be considered potential collision hazards. These asteroids are called “Near-Earth Objects” or NEOs, and 861 NEOs have a diameter of 1 kilometer or more. Thus far scientists have tracked over 1,400 “Earth-crossers” that pose a significant threat. But as the surprise arrival of the asteroid over Chelyabinsk, Russia demonstrated, we’ve not yet located every potential collider.

How often do astronomers expect an asteroid to hit Earth? What evidence do we have that asteroids have hit Earth in the past? Where else can we find most asteroids other than in the main belt? How do asteroids get named, and did you know there’s an asteroid named for a cat called Dr. Spock? That’s weird.

ASTEROIDS GOOD AND BAD

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Ceres, the largest asteroid, first discovered in 1801 by Giuseppe Piazzi, and visited by the Dawn spacecraft in February, 2015. Those bright spots remain a mystery, and Dawn continues taking pictures of Ceres from its closest approach, which continues the next few months. Image from NASA JPL via Dawn.

NASA’s new 2016 budget includes money for two asteroid missions. One of those missions continues an effort underway for years, the detection of near-Earth objects (NEOs), asteroids that pose a risk of colliding with our home planet. The other mission proposes to land on a near-earth asteroid, pick up a large boulder from its surface, and redirect the boulder into an orbit around the Moon. Once in a stable lunar orbit, manned missions would visit the asteroid fragment and retrieve pieces to return to Earth for detailed study.

Both missions complement each other and serve multiple roles. The detection mission will help protect Earth from a potentially cataclysmic collision with an asteroid. It’s happened many times in the past, and it continues to happen now. The biggest recent impact came in 2013 over Chelyabinsk, Russia, from an asteroid estimated at a mere 18 meters in diameter.

The detection mission would also help NASA find a nearby asteroid from which it might pluck a piece. That mission to “redirect” a piece of an asteroid into orbit around the Moon would build our understanding of what asteroids consist of and how they might contribute valuable minerals for industry. Perhaps even more important, the “redirect” mission involves landing on an asteroid and moving a piece of it onto a different trajectory, skills we would need if we ever detected an asteroid on a collision course with Earth and wanted to deflect it away.

How many asteroids are out there? How big are they? How many are on a course that might bring them into contact with Earth one day? What are they made of and does their composition mean we might benefit by capturing one and mining it? Could we deflect an asteroid on a collision course with Earth? What spacecraft missions have already studied asteroids, and what have we learned?

Stay tuned.

 

What Are the Odds?

It’s my birthday, and Dave’s and Mary’s and Sean’s too! We’re in a neighborhood dinner group consisting of six couples. One evening a few years ago we came to the rather amazing discovery that of the twelve of us, four shared a March 18th birthday.

Now the chance that two people meeting on the street would share the same birthdate, say, March 18, is 1 in 365. The chance that three people would share the same birthday is 1 in 133,226. Add a fourth person and the odds are only 1 in 48 million they would share the same date of birth.

But the odds that those four don’t share just any date, but share March 18, drop to 1 in 17 trillion. Hey, it’s a special date!

If we assume the world population is about 7.3 billion, and we divide that entire world population randomly into little groups of four, there would be 1.83 billion such groups. If you did that grouping-by-four many different times and kept track each time how many of the 1.83 billion groups had all four members sharing the same birthdate (any date), you would expect an average of 38 such groups with each grouping.

The chance that among those 1.83 billion groups of four there existed one group of four that shared a March 18 birthday is 1 in ten thousand. That is, you would expect to have to regroup the world’s entire population 27 times to get one group of four that shared a March 18 birthdate. And the four of us live within a couple blocks of each other and get together every other month to share a meal with our wives and husbands.

The world sometimes turns out to be stranger and smaller than you imagined.

Risk: not a game

One’s perception of risk doesn’t always match up well with the reality. Today, the sixth of October in the year two thousand and fourteen, the risk of Ebola dominates the news. It seems to be a scary time. This perceived risk has persuaded some elected politicians to call for travel bans, something you don’t hear about very often. So the risk must be extreme, right?

So far, one person with Ebola entered the United States. There may be a few more, even several more or a dozen or so before the crisis in west Africa is contained. But for perspective, last year’s flu season here saw 58,732 confirmed cases of flu serious enough to require hospitalization. Last year, 108 children died from the flu in the United States alone. Although it’s difficult to get a firm count, the total death toll from the flu here ranges from 3,000 to 49,000 every year.

The flu virus can spread from a cough or a sneeze, something Ebola cannot do. Ebola is more deadly than the flu if you catch it, but it’s not easily spread. Ebola is out of control in west Africa because it’s a desperately poor region with little capacity to deal with something new. Public health doctors here insist that the best way to protect the rest of the world from the Ebola virus is to snuff it out in west Africa where its numbers have mushroomed. Travel bans will only make it more difficult to send the health care workers needed there to stop the virus in its tracks. And given the slow and poor transmission ability of Ebola, screening travelers is a highly effective containment tool. Such screening would not be nearly so effective with the flu.

In the meantime, if you’re really worried about you or your kids catching a virus and getting sick, get a flu vaccination and keep your kids’ mumps, measles, and rubella and other vaccinations up to speed.

DISRUPTION: A review of the climate change documentary

The video opens with the following quote:

“Power concedes nothing without a demand. It never did and it never will.
—Frederick Douglass

This statement and its author tell us much about the documentary that follows. The focus is on action, in keeping with the title itself, Disruption. The target of the action is, clearly in this case, the fossil fuel industry and the political machine that protects and supports it. And quoting Frederick Douglass hints at the central environmental justice theme.

As a scientist, I am nervous when the discussion moves from a consideration of the science to how to achieve political goals. So, yes, I am not thrilled with the documentary’s fuzzy use of the “tipping point” concept, and avoidance of the more accurate term, “positive or reinforcing feedback.” Yes, I am anxious when specific storm events come to characterize climate change rather than global shifts in heat content of the oceans and the atmosphere. Yes, I am concerned with the touch of exaggeration I perceived when methane was described as fifty times more potent a greenhouse gas than carbon dioxide (I believe twenty-five times is more like it). And I don’t understand why they left out sea level rise and long-term climate events like drought.

However, as a parent and a new grandparent I am more nervous with the risks we take doing nothing, or doing as little as we have done for the past decade to avert climate change. The risk is significant, the consequences likely to be severe, and many unknowns exist that could send us spiraling down paths to new unpleasant, perhaps catastrophic “normals” we could find difficult to avoid or change. I don’t want that for my children or their children.

The purpose of this documentary was not so much education as motivation. The clear goal was to spur individuals to take part in the upcoming climate change march in New York City, either directly or in their local community. Given the seriousness of the problem and especially our country’s negligence in taking sufficient steps to address climate change, I can live with a little rabble-rousing. I only wish it were done with more dispassionate logic, but passion is what they hope, and need, to arouse. On that point I have no dispute.

Next to large crowds on the streets, neighbor to neighbor efforts to share knowledge of the causes and consequences and solutions to climate change seem important as well. Consider participating in that type of activity in addition to marching in the streets.