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

I got a few interesting questions about my first Apophis post

“Why not wait with a mission until after 2029, then it will be clearer if the Earth might be hit in 2036”
“Is it a coincidence that there are exactly seven years between the two data?”

Here is a bit more information. For some of you it may be a bit (too) technical ..:-) Don’t worry.

The present orbit of Apophis is shown in the figure below as the blue line, together with the orbits of Mercury, Venus and Earth, with the Sun in the center.
Distances are given in Astronomical Units (AU), where 1 AU = ~ 150 million km, the average distance between Earth and Sun.
Apophis has a period of  323.6 days, six weeks shorter than a year, and its orbit is quite elliptical, coming almost as close as the orbit of Venus, but also crossing the Earth orbit.

During an orbit Apophis crosses the Ecliptic twice. One crossing is no problem, but the other one is, because there it crosses the Earth orbit as well!
And Apophis, with its shorter period, is continuously overtaking Earth…..

The images come from an interesting NASA website where you can follow the course of Apophis in time.
Try it out and check that both Earth and Apophis will arrive at the Danger Point on 13-4-2029!

On that day Apophis will pass Earth at a distance of about 30.000 km and because of the Earth gravitation its orbit will be strongly disturbed.
It will get a boost from the encounter, increasing its orbit and its period. See the sketch below.

The uncertainty in the trajectory is indicated, the white bar is about 1000 km at present.

So, no need to worry about 2029. But there IS a (small) chance that Apophis might hit Earth exactly seven years later!
This could happen if Apophis, after deflection, enters into a resonant orbit with Earth.

What are resonant orbits? Two orbits are resonant if there is a simple relation between their respective periods, like 2:3, 5:6 etc
Example: two planets A and B with periods of 300 and 450 days have resonant orbits (2:3). Starting from any given position, they will be in exactly the same position after 900 days (A will have completed 3 orbits, while B has completed 2).

Back to Apophis.

There is a possibility that on 13-4-2029 Apophis will be deflected into a (6:7) resonant orbit! In that case it might hit Earth exactly 7 years later, having completed 6 orbits itself.

This will only happen when Apophis will pass through a very small “window” during its encounter with Earth in 2029. Estimated width about 600 meter(!) only. Astronomers call it a keyhole  🙂
Remember, Apophis has a size of ~ 300 m, so it just fits in the keyhole….

At this time the estimated probability that Apophis will pass through the 6:7 resonance keyhole is only about 1:250.000. Almost negligible .

Why is it then that for example the Russian Space Agency is still proposing a mission?
Well, if more accurate calculations in the coming years show that Apophis will pass through the keyhole, it will be rather easy to steer the asteroid away from it. As the keyhole is so small, just a few hundred meters will do.
That will be orders of magnitude easier than steering it away from the Earth, once it has passed the keyhole!

One last remark.
There was a question if a second hit, again on April 13, took into account leap years.
It does. A year is 365.25 days, so seven years equals 2556.75 days. And between 13-4-2029 and 13-4-2036 there are 2557 days (7 x 365 + 2 leap days).
Difference is only 6 hours. By the way 13-4-2036 will be a Sunday. Easter Sunday..:-)

A few days ago there was a news item about a proposal by the Russian Space Agency that they were considering a mission to this asteroid to deflect its course, because there is a risk that it might hit the earth in 2036.
Most asteroids orbit the Sun between Mars and Jupiter, but not all of them. Those with Earth-like orbits are monitored, because they might collide with the earth, with devastating consequences.

On 19-6-2004 an asteroid was discovered, which might collide with the earth in 2029. It was named Apophis, after the demon of darkness and chaos in Egyptian Mythology.
More accurate observations followed, and showed that this asteroid will NOT hit the Earth in 2029, although it will pass the Earth on Friday, April 13 (yes!) 2029 at a distance of only 30.000 km.
Mind you, that is closer than the altitude of the TV-satellites, circling the Earth!

At such a close distance the course of Apophis will be disturbed by the Earth. Calculations show that there is a small probability that at their next encounter, on Sunday, April 13 2036, Apophis could hit the earth. The estimated size of this asteroid is about 300 m and an impact could release an energy of ~ 900 megaton TNT (the Hiroshima atomic bomb was ~ 15 kiloton TNT, 60.000 times smaller!)

Here is the estimated risk path for such a collision

No wonder that it is the Russian Space Agency coming with this proposal.

When you want to know more about how to deflect such a massive piece of rock, there is a really fascinating educational website  about asteroids, Apophis, and how to deflect it. Choose the Expert option.