Writing in The Astrophysical Journal last month, Artie P. Hatzes, the director of the Thuringian State Observatory in Tautenburg, Germany, who was not part of the original discovery team, reported that he could not confirm the planet when he went looking for it in the European data on his own. “Sometimes it is there, other times not,” depending on the method he used to reduce the statistical noise, he said in an e-mail.
That doesn’t mean the planet does not exist, Dr. Hatzes wrote, but “in my years of experience in extracting planet signals, this simply does not ‘smell’ like a real planet.”
Dr. Hatzes’s skepticism proved catching. Suzanne Aigrain of Oxford University quoted Carl Sagan’s dictum that extraordinary claims require extraordinary evidence, saying that Dr. Hatzes’s paper “certainly casts doubt on the original evidence.”
Xavier Dumusque of the University of Geneva, who led the original discovery effort, said that Dr. Hatzes’s challenge was healthy for science. “Calling to question a detection is always something fruitful,” Dr. Dumusque wrote in an e-mail. But he added that it was clear in his team’s paper that “the signal we are searching for is at the limit of the data precision.”
More data, everyone agrees, is essential, and luckily there will be more data, according to Debra Fischer, a Yale astronomer who has studied the Alpha Centauri system. Both her group and the Geneva team of which Dr. Dumusque is a member obtained more observations in May.
Hubble's keen vision detected a mysterious gap in a vast protoplanetary disk of gas and dust swirling around TW Hydrae. The gap is 1.9 billion miles wide and the disk is 41 billion miles wide. The gap's presence likely was caused by a growing, unseen planet that is gravitationally sweeping up material and carving out a lane in the disk, like a snow plow.
The planet is estimated to be relatively small, at 6 to 28 times more massive than Earth. Its wide orbit means it is moving slowly around its host star. If the suspected planet were orbiting in our solar system, it would be roughly twice Pluto's distance from the sun.
Planets are thought to form over tens of millions of years. The buildup is slow, but persistent as a budding planet picks up dust, rocks, and gas from the protoplanetary disk. A planet 7.5 billion miles from its star should take more than 200 times longer to form than Jupiter did at its distance from the sun because of its much slower orbital speed and the deficiency of material in the disk. Jupiter is 500 million miles from the sun and it formed in about 10 million years.
TW Hydrae is only 8 million years old, making it an unlikely star to host a planet, according to this theory. There has not been enough time for a planet to grow through the slow accumulation of smaller debris. Complicating the story further is that TW Hydrae is only 55 percent as massive as our sun.
"It's so intriguing to see a system like this," said John Debes of the Space Telescope Science Institute in Baltimore, Md. Debes leads a research team that identified the gap. "This is the lowest-mass star for which we've observed a gap so far out."
An alternative planet-formation theory suggests that a piece of the disk becomes gravitationally unstable and collapses on itself. In this scenario, a planet could form more quickly, in just a few thousand years.
Kepler-22b is a planet with a 95 percent probability of being in its parent star’s habitable zone. Around 620 light-years away from us, it has a radius about 2.4 times as large as Earth, and is about 10 percent as massive as Jupiter. With that size, it’s most likely to be a gas giant.
Unfortunately, no moon was found around Kepler-22b. If it has any moons at all, they must be smaller than half Earth’s mass. Nonetheless, this was far from a wasted exercise. Planet hunters now have a small arsenal of tools and techniques at their disposal — enough for Kipping and his colleagues to draw the conclusion that if any Earth-like moon is there to be found around similar planets, they will find it.
Planet Kepler-22b was chosen for this search for several reasons. As well as being comfortably in the habitable zone and having been confirmed by Kepler observations, this planet also had radial velocity data available for it, and the observations contain very low noise (take it from me, noise in observations is the bane of an astronomer’s life!).
While no Earth-like exomoons could be found around Kepler-22b, the fact that moons should be very easy to see if they’re there is heartening. What’s more, it’s worth bearing in mind that this does not mean that Kepler-22b has no moons at all. For example, Titan, Saturn’s giant moon, has only 2 percent the mass of Earth.
We find no evidence for an Earth-like exomoon around Kepler-22b and yet have shown that the present data can easily detect such an object via signal injection. Current observations therefore dictate that Kepler-22b does not possess an Earth-like habitable moon. Our results then, combined with the very robust measurement of the planet’s radius, mean that Kepler-22 does not possess an Earth analog. This does not mean that the system possesses no options for an inhabited world, with notable possiblities being a smaller, presently undetectable moon (e.g. MS∼0.2M⊕) or a possible ocean on Kepler-22b. However, it is now clear that this is not the location to find a second Earth.
Could post independence governments in Africa have performed better? Perhaps, but at a price; they should have aimed at preserving their limited capacity; using it only sparingly. Instead, most governments in Africa moved fast to elaborate public functions. Botswana avoided this mistake perhaps because it had had an almost absentee colonial state. This could have reduced the demands for rapid africanisation. But acting like Botswana would have been a purely technical response to what was actually a burning political problem.
The nationalist struggle for independence emerged to challenge legally sanctioned exclusion of Africans from state power outside of traditional institutions in colonial Africa. That was its fuel. Upon independence, the first demand therefore was rapid africanisation. Although technically disastrous, it was politically popular. The second demand was derived from the first. Africans wanted to take public services to the wider population. Few governments would have survived by resisting this demand.
Political pressure for africanisation undermined the meritocratic systems of external recruitment and internal promotion that allowed the civil service to uphold its high standards. Rapid elaboration of functions without existing capacity made a bad situation worse. What was politically right was technically disastrous. And in our ethnically heterogeneous polities, promoting social inclusion – even on the face of things – was more politically desirable than sustaining technical competence. The problem is that it eroded competence and allowed cronyism and corruption to flourish. Politics is costly and Africa had to pay that price.
Many African elites focus on technical failures in Africa and ignore the political compromises that brought that failure. In other words, the price of political compromise was technical failure. It is possible that if such compromises had not been struck, many states in Africa would have collapsed under the weight of civil war. It is remarkable that African leaders who inherited fictions of states left behind by colonial rule were successful at creating a common national consciousness. This has sustained the sovereignty and territorial integrity of these nations. Today, few states in Africa have fallen apart like Somalia. In others, the state may not be omnipresent yet, but the concept of nationhood has gained a lot of ground.
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