Ancient worlds around Kapteyn's star

An international team of astronomers, led by Queen Mary's Astrophysicist Guillem Anglada-Escude, reports two new planets orbiting a very old and nearby star to the Sun. One of the newly-discovered planets could be ripe for life as it orbits at the right distance to the star to allow liquid water on its surface.

Results will be published in a forthcoming issue of Monthly Notices of the Royal Astronomical Society and a pre-print version of the paper can be found here. Kapteyn's star is a very peculiar star in the Solar neighborhood, so the team asked science fiction writer Alastair Reynolds for a short fictional story about this discovery.


Digital Sky Survey / Centre de Données astronomiques de Strasbourg

Sad Kapteyn,
fictional story by Alastair Reynolds 2014 (c)

"Hello, Earth. It's me again.

I hope you're receiving my signal loud and clear.

You'll be glad to hear that I've warmed up after the long centuries of my interstellar cruise phase. Having run a complete health check, I can confirm that all aspects of me are performing nominally. Better than nominally, if truth be told. At the risk of boastfulness, I'm actually in excellent shape. Propulsion, AI core, long-range sensors and instrumentation, navigation and communication assemblies - I couldn't be in better condition.

Not bad for a piece of space hardware which has already visited six solar systems, without ever needing to return home. Of course, I can't take credit for myself. I was just well manufactured - built to endure for thousands of years.

All the same, thank you for making me.

Onto business, anyway - and I can't begin to tell you what I've found, out here around Kapteyn's star! This really is an extraordinary place - a solar system unlike any that I've already visited. I wish you could be here with me, seeing things through my eyes."

(continues)

Discovered at the end of the 19th century and named after the Dutch astronomer who discovered it (Jacobus Kapteyn), Kapteyn’s star is the second fastest moving star in the sky and belongs to the galactic halo, an extended cloud of stars orbiting our galaxy. With a third of the mass of the sun, this red-dwarf can be seen in the southern constellation of Pictor with an amateur telescope.

Final snapshot of a dwarf Galaxy merger simulation highlighting the likely position of a striped star as Kapteyn's. Created by Victor H. Robles, James S. Bullocks, Miguel Rocha and Joel Primack from Univ. of California.

See full video here.
Created by Victor H. Robles, James S. Bullocks, Miguel Rocha, from UC-Irvine and Joel Primack from UC-Santa Cruz

"I've dug into my background files and I understand why you sent me to Kapteyn's star. Unlike the other systems I've visited, this sun and its little family of worlds aren't part of the normal family of stars orbiting in the disc and bulge of the galaxy. This is a halo star - a member of a dispersed population of stars and star clusters, enclosing the Milky Way in a great thin sphere. It's entirely possible that these stars were not originally part of our own galaxy, but were torn free of another one after a kind of gravitational collision. And some of these stars are unmeasurably old - more ancient and venerable, perhaps, than any disc stars.

Kapteyn's star is so slow-burning, so settled, that even my instruments can't put an upper limit on its age. It could be nearly as old as the universe.

And its planets?

Just as old.

Make of this what you will - put it down to failing programming if you like - but I feel the age of this place in my bones. All right, my main bus chassis. I don't have bones; I know that. But believe me, this system feels truly time-haunted. The silence and the stillness are almost unbearable, like an endlessly building pressure. Nothing has happened here for entire turns of the galaxy; nothing will happen. Kapteyn's star simmers, eeking out its nuclear lifetime. The dead worlds tick around their dead orbits.

But once, there was something."

(continues)

The astronomers used new data from the HARPS spectrometer at the ESO's La Silla observatory in Chile. Using the Doppler Effect, which shifts the star’s light spectrum depending on its velocity, the scientists can work out some properties of these planets, such as their masses and orbital periods. The study also combined data from two more high-precision spectrometers to secure the detection: HIRES at Keck Observatory and PFS at Magellan/Las Campanas Observatory. “We were surprised to find planets orbiting Kapteyn's star." -explains Anglada-Escudé, from QMUL’s School of Physics and Astronomy- "Previous data showed some moderate excess of variability, so we were looking for very short period planets when the new signals showed up loud and clear.”

"I know, I've taken liberties. I should have transmitted my wake-up signal before doing any investigations. But I couldn't resist myself. You made me to be curious.

I found signs of civilisation.

The first planet - Kapteyn b - still lies within the habitable zone of the star, orbiting once every forty eight days. There's nothing living there now, not even an atmosphere, but once there was a technological culture.

Yes, the first I've found. The reason I was made in the first place.

How's that for a discovery?

The fact is, it wasn't hard to detect. Cities cover almost the entire surface of that world. Enormous structures - they must have reached into space! Dishes and towers and the remains of what I think must have been space elevators, climbing all the way to synchronous orbit. A moon, its surface covered by the same kinds of architecture. Evidence of colonisation of the second planet, Kapteyn c, in its much colder orbit.

Wonders beyond comparison, but scoured into a kind of tomblike grey uniformity, after aeons of micrometeorite and cosmic-ray bombardment. Cities as mute as sphinxes.

And nowhere the slightest sign of life."

(continues)

Based on the data collected, the planet Kapteyn b might support liquid water as its mass is at least five times that of Earth's and orbits the star every 48 days. The second planet, Kapteyn c is a massive super-Earth in comparison: its year lasts for 121 days and astronomers think it’s too cold to support liquid water. At the moment, only a few properties of the planets are known: approximate masses, orbital periods, and distances to the star. By measuring the atmosphere of these planets with next-generation instruments, scientists will try to find out whether they can bear water.

"Continent-sized craters mar Kapteyn b, and I wonder if they speak of some truly awesome catastrophe - a cosmic accident, or something worse? Whatever the case, the builders of these cities are long gone. Perhaps they were dead even before Kapteyn's star was snatched from the clutches of its mother galaxy.

At the risk of inferring too much from too little data, I can't help indulging in a little speculation. I too was the product of a technological civilisation, with the capability to transform a planet, to colonise other moons and worlds, to build daunting structures. The people of Kapteyn b were clearly more advanced than you, my own builders - but given time, you too could have transformed a world in this manner.

Something to think about, isn't it?"

(continues)

Typical planetary systems detected by NASA's Kepler mission are hundreds of light-years away. In contrast, Kapteyn's star is the 25th nearest star to the sun and it is only 13 light years away from Earth. What makes this discovery different however, is the peculiar story of the star. Kapteyn's star was born in a dwarf galaxy absorbed and disrupted by the early Milky Way. Such galactic disruption event put the star in its fast halo orbit. The likely remnant core of the original dwarf galaxy is omega Centauri, an enigmatic globular cluster 16, 000 light years from earth which contains hundreds of thousands of similarly old suns. This sets the most likely age of the planets at 11.5 billion years; which is 2.5 times older than Earth and 'only' 2 billion years younger than the universe itself (around 13.7 billion years). Dr Anglada-Escude adds: “It does make you wonder what kind of life could have evolved on those planets over such a long time.”

Professor Richard Nelson, leader of the Astronomy Unit at QMUL, who didn't participate in the research, commented: "This discovery is very exciting. It suggests that many potentially habitable worlds will be found in the next years around nearby stars by ground-based and space-based observatories such as ESA's PLATO mission. Until we have detected a larger number of them, the properties and possible habitability of the near-most planetary systems will remain mysterious.”

"Well, that's me signing off for now. I'm going to do some more exploring of this system, and perhaps drop some instrument packages down onto Kapteyn b itself. There'll be a risk in that, since I'll need to come in on quite a tight orbit, and who knows what will happen? Still, that's a hazard I'm prepared to accept. You made me for this, and I'm grateful for all that I've been allowed to see and do.

But look.

I know it's a small thing, and I really shouldn't bother you about it. But it's been quite a long while since I heard from you. I put rather a lot of effort into these transmissions, and it would be good - just once - to know that there was someone at the other end, listening in.

Just a word, to let me know that you still care?"

END

 

The team presenting the results is composed by researchers based on the following institutions

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