注册 登录  
 加关注
   显示下一条  |  关闭
温馨提示!由于新浪微博认证机制调整,您的新浪微博帐号绑定已过期,请重新绑定!立即重新绑定新浪微博》  |  关闭

麦烧历险记

爱科学、爱生活──和我联系maishaoshao@gmail.com

 
 
 

日志

 
 

The Lure of Rocks From Outer Space  

2009-03-09 14:47:46|  分类: great feast |  标签: |举报 |字号 订阅

  下载LOFTER 我的照片书  |

In case you missed it, an asteroid — 2009 DD45 to be exact — measuring between 20 and 30 yards in diameter, flew past us on Monday at about 41,000 miles from Earth, which is about twice as high as the orbits of some telecommunications satellites. A more sizable asteroid, 99942 Apophis, which has a 885-foot diameter, will come within 21,000 miles of the Earth in 2029.

We have always been fascinated by these romantic, menacing objects in the sky — they have been the stuff that grips us to our seats in movie theaters or takes us out into the backyard with a telescope on a starry night. What is it about asteroids that capture our attention?

The Bugaboos of Our Solar System

The Lure of Rocks From Outer Space - 麦烧 - 麦烧历险记

SETI Institute in Mountain View, Calif. He is the author, most recently, of “Confessions of an Alien Hunter.”

Let’s face it, asteroids are like sharks and tigers: we like them because they’re big and dangerous.

Of course, not every scientist will own up to such a dramatic motive for studying these potato-shaped projectiles. Instead, they’ll offer incentives that seem less visceral, less sensational, and less tied to these rocks’ potential malevolence. Asteroids are, after all, relatively pristine remnants from 4.6 billion years ago when the Sun and its retinue of planets, moons and lesser bodies were born. Studying asteroids can, and has, given us clues as to how our solar system came to be — a fundamental puzzle for science.

Asteroids might even tell us something important about our own presence. They are chock-a-block with carbon compounds that could have played a crucial role in seeding our planet with the raw ingredients of life. A storm of asteroids billions of years ago left the moon unattractively pockmarked, but might have jump-started the emergence of Earth’s flora and fauna. We might owe our existence to these nomads of the solar system, a humbling thought.

But while asteroids are good lab rats for research, it’s the fact that they can wreak havoc and destruction that makes them irresistible. The dinosaurs and three-quarters of everything else that crawled or slithered on land were obliterated when a rock the size of San Francisco slammed into the Yucatan 65 million years ago. There are plenty of similar-sized asteroids still out there, and several will have our name on them. If we wait long enough, a disaster that outranks such trendy concerns as nuclear war, pandemics or environmental degradation will strike our planet again.

It’s danger leavened with a dare: namely, that our three-pound brains can do what the dinosaurs couldn’t — avoid destruction from the skies. By the immensity of their threat, asteroids provide us the chance to be the ultimate heroes.

An Asteroid’s Thrill Factor

The Lure of Rocks From Outer Space - 麦烧 - 麦烧历险记

Strange Horizons, and was co-editor of the anthology, Twenty Epics. She teaches history at a private high school in New York.

We’re used to thinking of our universe as a calm and orderly place, a predictable place. We know, down to the minute, when the sun is going to rise and set. We have such thorough knowledge of the movements of the stars that we can create an image of the sky over Brooklyn on this date 2,000 years ago.

Yet still, every so often we get a reminder, in the form of an asteroid, that the universe remains unpredictable and unknown to us. This image of asteroids permeates fictional narratives as well. In science fiction, asteroids are often used as a counterbalance to the power of science and technology. In “Star Wars” and “Star Trek” and countless similar stories, when our scrappy heroes are on the run from enemy forces, asteroid fields level the playing field.

In big disaster movies like “Armageddon” and “Deep Impact,” humans discover that neither fancy technology nor powerful militaries can necessarily save us from a big space rock. (By the same token, the image of asteroids in science fiction taps into a longing for vanishing frontiers, which has its echoes of cowboy fiction.)

Of course, when you’re dealing with the unknown and unpredictable, there’s also the potential for danger. Asteroids violate our sense of the natural order every time they slip loose from their regular orbits and head toward us.

And they have, in fact, played a role in Earth’s history — an asteroid impact killed the dinosaurs, after all. In 1908, at Tunguska, Russia, an asteroid had an explosive impact comparable to a fusion bomb — astronomers estimate that impacts at that size happen once every few hundred years.

But an impact like the one that killed the dinosaurs happens once every 10 million years or less. This puts asteroids at a sweet spot for the thrill factor, kind of like a roller coaster. Your rational brain can run the numbers and realize that, realistically, you’re really not going to die, but your irrational brain can enjoy being a little scared.

The Torino Scale Shows We’re Safe

The Lure of Rocks From Outer Space - 麦烧 - 麦烧历险记

is a senior research scientist and manager of NASA’s Near-Earth Object Program Office. He has written four books on comets and asteroids, and asteroid 2956 was renamed 2956 YEOMANS in his honor.

There was never any chance that the small asteroid, 2009 DD45, would strike us. But there’s always interest in such events because these near-Earth objects — the rocky asteroids and icy comets that can come within 30 million miles of the Earth’s orbit — are our closest neighbors.

We owe our very existence and current position atop the food chain to these celestial visitors. As relatively unchanged remnants of the solar system formation process, they were the vessels that carried to the early Earth much of the carbon-based materials and water that allowed life to form. Once life did form, subsequent collisions punctuated evolution allowing only the most adaptable species (for example, mammals) to evolve further.

Being showered by celestial matter is an every day occurrence. A few basketball-sized asteroids fall to Earth every day, along with an endless stream of cometary dust and pebble-sized particles, which we see as shooting stars. Volkswagen-sized asteroids hit the Earth’s atmosphere a few times each year.

In fact, a spectacular fireball lit up the predawn sky above northern Sudan on Oct. 7, 2008. That explosion was caused by the atmospheric entry of a small asteroid, estimated to be no more than a few meters in diameter, which very likely scattered fragments across the Nubian desert below. Such impact events are not uncommon, but this case was unprecedented because astronomers at the Catalina Sky Survey near Tucson, Ariz., discovered the asteroid the day before it reached the Earth and the impact location and time were, for the first time, predicted in advance.

Small objects, less than 25 meters across, rarely survive atmospheric entry. But ones that are 1 to 2 kilometers would cause global problems. We believe there are about 950 objects larger than 1 kilometer in diameter, and to date, NASA’s Near Earth Object Program has found and tracked nearly 90 percent of them. None of them are a threat to Earth.

For people who worry that a strike could happen any time, there may be comfort to be found in our program’s Sentry Risk Table, which rates the risks from near-Earth objects for which we cannot yet rule out a future Earth impact. Most often, an object’s appearance on the risk page means its orbit is not accurately known so an encounter with Earth, though very unlikely, is still a remote possibility.

The Lure of Rocks From Outer Space - 麦烧 - 麦烧历险记

(Credit: NASA) Scale 0 and 1 from The Torino Impact Hazard Scale.

All future Earth impact possibilities are given a score from 0 to 10 on the Torino Scale. Of the 260 objects listed on the table, only one object — 2007 VK184 — has a score of 1, which is defined as representing no unusual level of danger, where “the chance of collision is extremely unlikely with no cause for public attention or public concern.” The rest have a score of zero.

Asteroid 2009 DD45 had a zero probability of impact and hence was never on the risk page. So while popular imagination might depict asteroids as threatening, so far, there is nothing to worry about.

When the Big One Hits, There Will Be No Need to Worry

The Lure of Rocks From Outer Space - 麦烧 - 麦烧历险记

Neil deGrasse Tyson, an astrophysicist, is the director of the Hayden Planetarium at the American Museum of Natural History in New York. He is the author of “Death By Black Hole” and “The Pluto Files.”

What is it about asteroids that grabs my attention?

That Earth plows through several hundred tons of space pebbles per day.

That thousands of much larger rocks circle the Sun on trajectories that cross Earth’s orbital path.

That one of these has enough impact energy to create trillions of dollars in property damage.

That another one of these has enough impact energy to disrupt civilization.

That yet another one of these has enough impact energy to render the human species extinct.

After which we will no longer have cause to worry about asteroids.

Everyone Loves a Good Drama

The Lure of Rocks From Outer Space - 麦烧 - 麦烧历险记

Loch Ness Productions, a company that creates content for planetariums, science centers and observatory outreach programs. She keeps a blog called The Spacewriter.

There’s no doubt that asteroids are attention-grabbers. Sci-fi filmmakers like them in particular because they combine two things that make good action cinema: outer space and danger. In a typical dramatic plotline, a big chunk of space rock is headed straight for somewhere like Manhattan. A lone hero rides out to do the Angry Earthman Mambo on the asteroid. He either dies trying or whacks the asteroid and returns to great acclaim (and gets the girl). End of story. Roll the credits.

The Lure of Rocks From Outer Space - 麦烧 - 麦烧历险记

(Credit: Reuters) An asteroid named Eros.

In real life, asteroids are key players in the ultimate reality action show — a drama that began some 4.6 billion years ago: the formation of the Sun and planets. Asteroids can tell us about that time because they are the leftovers, the stuff that was there, but didn’t quite make it into a planet. Oddly, one these denizens from our past could affect Earth’s future.

How so?

The orbits of some asteroids intersect Earth’s, creating a chance that we could be smacked by one that strays too close. Therefore, when the Earth-crossing asteroid 2009 DD45 was discovered a few days before its closest approach earlier this week, it was a big deal. Astronomers started calculating its trajectory and Planetary Society, UniverseToday, Sky and Telescope and Bad Astronomy began spreading the news.

Astronomers ask many questions when an Earth-crossing asteroid is discovered. How close will it come? Could this one hit us? If so, where will it hit? When will it hit? Answers to those last two are where drama and romance give way to cold physical reality. The chance of an object hitting our planet is not just a possibility. It’s a fact.

Stuff impacts Earth every day. Most of it does little damage. However, it’s only a matter of time before a large-enough Earth-crossing asteroid crashes into the planet. When it does, the resulting impact will affect everything on Earth, and not in a good way. Now THAT’S cosmic drama!

Our Friend in the Sky

The Lure of Rocks From Outer Space - 麦烧 - 麦烧历险记

Lewis Dartnell is an astrobiologist at University College London, researching the possibility of microbial life surviving on the surface of Mars.

When you hear about near-misses from asteroids like 2009 DD45, so-called near-Earth objects, your first thoughts might be of the apocalyptic. Hollywood has ensured that we are all fully aware of the risks posed to planet Earth from such space rocks, perhaps not to extinguish all life on our planet (it would take a truly Earth-cracking collision to wipe out the hardy bacteria living miles deep in the hot crust of our planet), but certainly collapse civilization as we know it.

Asteroids, which are rich in iron, may turn out to save humanity on Earth where natural resources are limited.

But it is important to not sensationalize such risks, and thankfully the news reporting of 2009 DD45 generally seems to have resisted such cheap hooks. The only recorded incident of an animal being killed by an extraterrestrial impact was a dog apparently struck by a shard of the Nahkla meteorite, a fragment of Mars that fell in Egypt in 1911. However, since there was only a single witness to the event, who claimed that the dog had been completely vaporized by the impact — leaving no trace — this apocryphal story is, shall we say, a mite difficult to actually verify.

In fact, asteroids may turn out to be the savior of humanity, not our nemesis. The resources provided by planet Earth are inherently limited, and the path to continued expansion might simply be to begin harvesting from beyond our world. Many asteroids are very iron-rich, and such a space rock of even modest size would yield more metal than that refined throughout all of human history. The financial rewards for successfully mining a metallic near-Earth object will be literally astronomical, and some of them would actually be easier to reach in terms of the energetics of space travel, than the Moon.

And as we become more skilled at rendezvousing with nearby asteroids, and in time learning how to nudge their orbits, we will earn the most valuable prize of all. We will become capable of protecting our homeworld from the hammer-fall of an errant lump of cosmic rubble.

comment:http://roomfordebate.blogs.nytimes.com/2009/03/06/the-lure-of-rocks-from-outer-space/?ref=science

  评论这张
 
阅读(657)| 评论(0)
推荐 转载

历史上的今天

评论

<#--最新日志,群博日志--> <#--推荐日志--> <#--引用记录--> <#--博主推荐--> <#--随机阅读--> <#--首页推荐--> <#--历史上的今天--> <#--被推荐日志--> <#--上一篇,下一篇--> <#-- 热度 --> <#-- 网易新闻广告 --> <#--右边模块结构--> <#--评论模块结构--> <#--引用模块结构--> <#--博主发起的投票-->
 
 
 
 
 
 
 
 
 
 
 
 
 
 

页脚

网易公司版权所有 ©1997-2017