15 February 2013: A small asteroid enters the Earth atmosphere over Russia. Mass ~11.000 tonnes, size ~20 m and speed ~18 km/s. At an altitude between 15-25 km it explodes, causing a shock wave on the ground resulting in about 1500 people hurt (mostly by scattered glass) and ~ 7000 buildings damaged. Estimated energy 440 kilotons of TNT,  equivalent to ~25  times the energy of the  atomic bomb on Hiroshima, most of it absorbed in the atmosphere. This asteroid had not been discovered before its impact.

On the same day  about 15 hours later, asteroid 2012 DA₁₄ passes Earth at a distance of only 28.000 km (that is within the orbit of the telecommunication satellites!). Bigger (about 40.000 tonnes and 30 m), it was discovered in February 2012. Although occurring almost simultaneously, the two events are not related.

Next year, 19-10-2014,  comet C/2013 A1 will pass extremely close to Mars, with a small possibility of an impact with the planet. Here we are talking about a different order of magnitude! Estimated size of the comet nucleus is ~ 3km! IF it would hit Mars, the energy released would be in the order of millions of Megatons of TNT. For comparison, the asteroid that struck Earth 65 million years ago and ended the dinosaur era on Earth  was only about three times as powerful.

Do we have to get worried? In the aftermath of the Chelyabinsk meteor there was a lot of commotion in the media that action should be taken immediately to protect us from future collisions. Suggesting that nobody had expected this. As if the scientific world was not already aware of this problem!

Those outer space objects (asteroids, meteorites, comets) that can come close to (or even hit) Earth are called Near Earth Objects (NEO’s). Because of the impact risk they are monitored already for decades. The problem is that there are many of them and that they come in all sizes. Here is a graph of their distribution. The blue line gives the number of known NEO’s, the red line is a estimate of their total number. Please note the double logarithmic scale of the graph! For example, only about 100 NEO’s with a size of ~10 meter have been observed, whereas the estimated total number is ~ 10 million!

At the moment about 10.000 Near-Earth objects have been discovered. About 900 of them are asteroids with a size of 1 km or larger.

Here is a table with (statistical) information about the impact of a NEO. The second row gives data for objects with a size of 30 meter. The 2012 DA14 falls in this category. The effect of impact: a fireball, a shock wave and minor damage. Fits quite well the Chelyabinsk meteor, although it was smaller. The second column gives the average time in years between impacts of this size: 300 year.

If comet C/2013 A1 would have been on a (near) collision course with Earth, it would fall in the category: Billions of people dead, global climate change. Time interval: millions of years.

Followers of my blog may remember the post about Apophis At the time of discovery there was worry that it might hit Earth. We know now that the probability of impact is negligible. With its estimated size of 300 m it would create havoc, but no global destruction.

If a NEO on collision course is discovered early enough, it may be possible to deflect it. Numerous proposals exist. See my post Paintballing Apophis or do a Google search on “deflecting a NEO”

Conclusion: Earth runs a risk of an impact with a NEO. It is not a matter of IF but of WHEN. Early observation of “dangerous” NEO’s is important, so protecting measures can be taken. That is why there are global initiatives, like for example  NEOShield

For this post graphs, tables etc have been taken from this very informative site.

Before I started blogging, I wrote emails to a group of friends, interested in science. Several of these emails I have, after editing, entered as posts for my blog.
The first email (and now the first post on this blog) was about Apophis, an asteroid, that will pass Earth in 2029 at a close distance, and might (with a chance of 1 to 250.000) collide with Earth 7 years later, in 2036

This is an artist impression of Apophis, diameter ~ 270 m with an estimated mass of 27 megatonnes.

A collision with the earth would be a catastrophe. The impact would be the equivalent of 900 megaton TNT, ~ 60.000 Hiroshima atomic bombs.

When Apophis was discovered in 2004, there was a brief period of concern that this asteroid might hit Earth in 2029. It will not, and even in 2036 the chance is almost neglegible

But there are thousands of asteroids with orbits that may bring them close to Earth, so called NEA‘s, and NASA has an observation program to monitor them.

What to do when an asteroid is discovered which is on a crash course with Earth? We will have to deflect it! How? Many solutions have been proposed. Send a rocket to the asteroid and detonate a nuclear bomb, or let the rocket crash itself against the asteroid. Or use a strong laser beam to deflect the course.When you do this while the asteroid is still far away, a tiny change in course could be sufficient.

For a couple of years already a yearly competition “Move an Asteroid” is organised by the Space Generation Advisory Council , for students and young (space) professionals.

This year the competition was won by a MIT graduate student, Sung Wook Paek.

His winning proposal:

Launch a rocket, with a cargo of 5000 kg of pellets, filled with white paint. When near the asteroid, fire two salvos of pellets, timed in such a way, that the (spinning) asteroid will be completely covered with a very thin layer of white paint.

Here are two screenshots of a YouTube clip, published by MIT. In the left picture two pellet clouds are approaching the asteroid.  In the right picture one cloud has painted one half of the asteroid white already.

The colliding pellets will change the course of the asteroid a little bit. That is not new, but the white paint is. The photons from the sun will reflect against this bright white surface, and this results in (additional) radiation pressure. Also a tiny effect, so this kind of action should be taken, many years before the asteroid comes close to the earth.

Cosmic paintball, what a nice idea!

It is quite a long time ago that I have reported to you about interesting science topics!
Much of this year has been quiet, but that might change. So expect a few posts..:-)

1. Probably you have heard about neutrino’s traveling faster than light? That would be a really shocking discovery, if true….
For the time being, personally I bet it is not true. I may write about it later
2. There are rumours going around that next week CERN, during a press conference, will announce evidence for the Higgs boson, a.k.a the God particle.
It might be lighter than expected.
3. The Nobel prize for physics has been awarded this year for a discovery, the importance of which can be explained easily to interested outsiders. I will write about it soon.

This postl is about the discovery of extra-solar planet Kepler 22b.

You may remember that I have written a post in September 2010, about another extra-solar planet, the Gliese 581 g  located in the habitable zone of its star.
By the way, when you follow the Wikipedia link, you will see that there is some doubt now if this planet  really exists.

In March  2009, a satellite has been launched with a mission to discover Earth-like planets orbiting other stars. It was named  , very appropriately,  the Kepler satellite

Here is the satellite, note the size of the humans

How to discover planets? The stars may be hundreds of light-years away. Planets will not be directly visible at that distance.
Here is the procedure followed by the Kepler mission:

1. When a star has a planet,  the orbit of this planet can be such that it passes between Earth and the star.
2. In that case, the amount of star light reaching the earth will be slightly reduced during passage of the planet.
3. Measure the light intensity of the star. If there are periodic (minuscule) dips, it could be because of a planet passing. This will give the period of the planet. How large the dip is, will tell us something about the size of the planet.
4. When you know the mass of the star, Kepler’s third law will give you the radius of the planetary orbit, so you can draw conclusions if the planet is in the habitable zone of its star.

An ambitious program, right?
In 2004, our own planet Venus passed between the Sun and Earth.
With a group of friends we have been watching the event. You must take precautions not to be blinded by the sunlight.
Here is what we managed to see. The black dot in the sun’s image is Venus.

The Kepler approach will be, to look at the intensity of the starlight and at the dip in this intensity during the passage of the planet.
Not easy. “This is akin to sensing the drop in brightness of a car’s headlight when a fruitfly moves in front of it“

Well, it works!!
Until now, more than two thousand of so-called Kepler Objects of Interest (KOI’s), have been found. Not all of those will be planets.
Here is a preliminary list of potential habitable planets, found until December 2011.

Now, do NOT be fooled by the “artist impressions” of these planets.The blueish, watery color of several candidates is not based on any factual information about the presence of water.
The Kepler data give information about the size of the planet and its location within the habitable zone. It’s amazing that this can be done, for a star that maybe at a distance of hundreds of lightyears, but that’s it, for the time being.

By the way, note that Gliese 581 d is still in the list (outer edge of the habitable zone), but Gliese 581 g is no longer mentioned.

And also Kepler 22-b is not there, because that is the recent discovery, announced last week, that caused so much excitement.

Why the excitement? Here is a sketch

a) The star Kepler 22 is very similar to our Sun, in size and temperature
b) Kepler 22-b is within the habitable zone of the star
c) The planet is still larger than earth, but not much larger. So it could be a rocky planet. (Large planets, Jupiter size, will be gaseous) A rocky structure and liquid water are often seen as prerequisites for the development of life.

Again, the image of Kepler-22b in the above picture is an artist impression!
Keep that in mind when you read  reports like Human-like Life Could Exist on Newly-discovered Planet
With this quote: “A newly-discovered Earth-like planet could very well contain continental features where normal human-like life could exist. Or it  could be more of a water world with an ocean containing life forms similar to dolphins”

Hm. Then I like this report better: Kepler 22b: probably not home to interesting aliens

Here are a few more links
The official website of the Kepler Mission ,well-designed, very interesting.
The website of the Planetary Habitability Laboratory

Do you want to help? Kepler is monitoring more than 150.000 stars, and is using computer software to look at recurring “dips” in the received starlight. A huge job. Humans are still better in pattern recognition. So why not become a planet hunter yourself?

Just two days after I had published my first post about life in the Universe, it was announced by two American astronomers, Vogt and Butler, that a new extrasolar planet has been discovered, the first one where life might be possible. See for example this New York Times article:

Reason for me to send publish an extra post, before I compose part two of the Great Debate post..

Gliese 581 is a so-called red dwarf star, located at a distance of 20 light-year from the Sun.
In itself a smallish nondescript star in our Milky Way, but interesting because it has been found that a number of planets orbit this star.
Four were known already, two more have been discovered now.
I have roughly given their position, size is not to scale. (keep in mind that the distance scale is logarithmic)

For comparison the Sun and some of its planets are also shown.
The blue band is the habitable zone, not too cold, not too hot, assuming water-based life.
Excitement is about planet g, right in the middle of Gliese’s habitable zone. This is a first. It has a mass of about 3 earth masses, and orbits Gliese in 37 days.

Only a pity, that the planet, like its 5 siblings, is tidally locked to Gliese, meaning that it always faces the same side to its sun (same as our moon is tidally locked to Earth). So it has a cold side and a hot side. If life exists there, it would probably be in the twilight zone