A new phase in the search for life elsewhere is about to begin
“WE’VE been wondering what planet we’re first going to look for life on. Now we know.” Rory Barnes, of the University of Washington, puts it nicely. Proxima Centauri, the star closest to the sun, has a planet. That planet weighs more or less the same as Earth and is therefore presumably rocky. And it orbits within its parent star’s habitable zone—meaning that its surface temperature is likely to be between 0°C and 100°C, the freezing and boiling points of water at sea level on Earth.
A prize discovery, then, for astrobiologists such as Dr Barnes. And the discoverers are a transnational team of astronomers who have been using telescopes at the European Southern Observatory (ESO) in the Atacama desert, in Chile, for planet-hunting. Though they have not seen the new planet directly (they have inferred its existence from its effect on its parent star’s light), their paper in Naturedescribes what they have been able to deduce about it.
Proxima Centauri b, as it is known, probably weighs between 1.3 and three times as much as Earth and orbits its parent star once every 11 days. This puts its distance from Proxima Centauri itself at 7m kilometres, which is less than a twentieth of the distance between Earth and the sun. But because Proxima is a red dwarf, and thus much cooler than the sun, the newly discovered planet will experience a similar temperature to Earth’s. It is not the only Earth-sized extrasolar planet known to orbit in a star’s habitable zone. There are about a dozen others. But it is the closest to Earth—so close, at four light-years, that it is merely outrageous, not utterly absurd, to believe a spaceship (admittedly a tiny one) might actually be sent to visit it. Before this happens, though, it will be subjected to intense scrutiny from Earth itself.
Eyeball to eyeball
That scrutiny will probably be led by ESO. The data which led to Proxima Centauri b’s discovery came from the observatory’s 3.6 metre telescope at La Silla, in Chile. But ESO is also building a much bigger device, the 39-metre European Extremely Large Telescope (E-ELT), at another site in Chile. Since the late 2000s Markus Kasper has led a team at ESO which is designing a specialised planet-spotting instrument, the Exoplanet Imaging Camera and Spectrograph (EPICS), to fit on this telescope. Dr Kasper’s camera has a price tag of €50m, and there have always been questions in the past about whether it is worth the money. But EPICS stands a better chance of producing actual pictures of Proxima Centauri b than any other camera in the world (or off it). Its future can now scarcely be in doubt.
The problem for astronomers trying to catch a glimpse of Proxima Centauri b is that, though close to the Earth by interstellar standards, it is even closer to its parent star by more or less every other standard short of that of walking down the road to the chemist. Seen from Earth, star and planet are 35 thousandths of an arc second apart (an arc second is a 3,600th of a degree). Producing a picture that separates the two objects thus requires a telescope with a resolution good enough to distinguish between the left and right headlights of an oncoming car in Denver from the distance of Berlin.
Things get worse. Dim as it is, Proxima Centauri (pictured above, as seen by the Hubble space telescope) is still more than 10m times brighter than its planet is expected to be. It is as though one of those headlights in Denver was actually the open door to a furnace, while the other was a tea light. This is what makes the E-ELT and EPICS crucial. EPICS contains a coronagraph—a tiny shield that blocks out a star’s light so that adjacent planets can be seen. Unfortunately, a coronagraph reduces a telescope’s resolution, meaning you need an even bigger one to see the target in the first place. To observe Proxima Centauri b using a coronagraph, and looking in the infrared wavelengths that are likely to provide the best information about its atmosphere, you need a telescope at least 20 metres across; 30 metres would be better.
Two other large telescopes besides E-ELT, of 27 metres and 30 metres diameter, are under construction and planned. But some suggest the first of these, the Giant Magellan Telescope, also in Chile, is not well suited to the use of a coronagraph, and the second, the Thirty Metre Telescope, is planned at the moment for Hawaii, which is in the northern hemisphere. Proxima Centauri is in the southern skies, and therefore not so easy to study from north of the equator.
There may, just possibly, be a short cut.
Photonics advances allow us to be seen across the universe, with major implications for the search for extraterrestrial intelligence, says UC Santa Barbara physicist Philip Lubin
Looking up at the night sky — expansive and seemingly endless, stars and constellations blinking and glimmering like jewels just out of reach — it’s impossible not to wonder: Are we alone?
For many of us, the notion of intelligent life on other planets is as captivating as ideas come. Maybe in some other star system, maybe a billion light years away, there’s a civilization like ours asking the exact same question.
Imagine if we sent up a visible signal that could eventually be seen across the entire universe. Imagine if another civilization did the same.
The technology now exists to enable exactly that scenario, according to UC Santa Barbara physics professor Philip Lubin, whose new work applies his research and advances in directed-energy systems to the search for extraterrestrial intelligence (SETI). His recent paper “The Search for Directed Intelligence” appears in the journal REACH – Reviews in Human Space Exploration.
“If even one other civilization existed in our galaxy and had a similar or more advanced level of directed-energy technology, we could detect ‘them’ anywhere in our galaxy with a very modest detection approach,” said Lubin, who leads the UCSB Experimental Cosmology Group. “If we scale it up as we’re doing with direct energy systems, how far could we detect a civilization equivalent to ours? The answer becomes that the entire universe is now open to us.
“Similar to the use of directed energy for relativistic interstellar probes and planetary defense that we have been developing, take that same technology and ask yourself, ‘What are consequences of that technology in terms of us being detectable by another ‘us’ in some other part of the universe?’” Lubin added. “Could we see each other? Can we behave as a lighthouse, or a beacon, and project our presence to some other civilization somewhere else in the universe? The profound consequences are, of course, ‘Where are they?’ Perhaps they are shy like us and do not want to be seen, or they don’t transmit in a way we can detect, or perhaps ‘they’ do not exist.”
Since the beginning of spaceflight, humans have accomplished wonderful feats of exploration and showcased their drive to understand the universe.
Yet, in those 60 years, only one spacecraft, Voyager 1 (launched in 1977) has left the solar system. As remarkable as this is, humans will never reach even the nearest stars with out current propulsion technology. Instead, radically new strategies involving the technology already available must be used.
We propose a roadmap to a program that will lead to sending relativistic probes to the nearest stars.
To do so requires a fundamental change in our thinking of both propulsion and our definition of what a spacecraft is. In addition to larger spacecrafts capable of human transportation, we consider “wafer sats”, wafer-scale systems weighing no more than a gram. The wafer sats would include integrated optical communications, optical systems, and sensors. These crafts, combined with directed energy propulsion, could be capable of speeds greater than 0.25 c.
This program has applications for planetary defense, SETI and Kepler missions.