Artist's impression of Proxima Centauri. Source European Southern Observatory, Press Release ESO2202, Reproduction allowed

Another Planet Discovered Orbiting Proxima Centauri

Guest essay by Eric Worrall

Proxima Centauri, our closest known stellar neighbour, is packed full of interesting planets. My question – when are we going to send a probe to take a look?

eso2202 — Science Release

New planet detected around star closest to the Sun

10 February 2022

A team of astronomers using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile have found evidence of another planet orbiting Proxima Centauri, the closest star to our Solar System. This candidate planet is the third detected in the system and the lightest yet discovered orbiting this star. At just a quarter of Earth’s mass, the planet is also one of the lightest exoplanets ever found.

The discovery shows that our closest stellar neighbour seems to be packed with interesting new worlds, within reach of further study and future exploration,” explains João Faria, a researcher at the Instituto de Astrofísica e Ciências do Espaço, Portugal and lead author of the study published today in Astronomy & Astrophysics. Proxima Centauri is the closest star to the Sun, lying just over four light-years away.

The newly discovered planet, named Proxima d, orbits Proxima Centauri at a distance of about four million kilometres, less than a tenth of Mercury’s distance from the Sun. It orbits between the star and the habitable zone — the area around a star where liquid water can exist at the surface of a planet — and takes just five days to complete one orbit around Proxima Centauri.

The star is already known to host two other planets: Proxima b, a planet with a mass comparable to that of Earth that orbits the star every 11 days and is within the habitable zone, and candidate Proxima c, which is on a longer five-year orbit around the star.

Proxima b was discovered a few years ago using the HARPS instrument on ESO’s 3.6-metre telescope. The discovery was confirmed in 2020 when scientists observed the Proxima system with a new instrument on ESO’s VLT that had greater precision, the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO). It was during these more recent VLT observations that astronomers spotted the first hints of a signal corresponding to an object with a five-day orbit. As the signal was so weak, the team had to conduct follow-up observations with ESPRESSO to confirm that it was due to a planet, and not simply a result of changes in the star itself.

After obtaining new observations, we were able to confirm this signal as a new planet candidate,” Faria says. “I was excited by the challenge of detecting such a small signal and, by doing so, discovering an exoplanet so close to Earth.”  

At just a quarter of the mass of Earth, Proxima d is the lightest exoplanet ever measured using the radial velocity technique,surpassing a planet recently discovered in the L 98-59 planetary system. The technique works by picking up tiny wobbles in the motion of a star created by an orbiting planet’s gravitational pull. The effect of Proxima d’s gravity is so small that it only causes Proxima Centauri to move back and forth at around 40 centimetres per second (1.44 kilometres per hour).

This achievement is extremely important,” says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile. “It shows that the radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.

This result clearly shows what ESPRESSO is capable of and makes me wonder about what it will be able to find in the future,” Faria adds.

ESPRESSO’s search for other worlds will be complemented by ESO’s Extremely Large Telescope (ELT), currently under construction in the Atacama Desert, which will be crucial to discovering and studying many more planets around nearby stars.

More information

This research was presented in the paper “A candidate short-period sub-Earth orbiting Proxima Centauri” (doi:10.1051/0004-6361/202142337) to appear in Astronomy & Astrophysics.

The team is composed of J. P. Faria (Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Portugal [IA/UPorto], Centro de Astrofísica da Universidade do Porto, Portugal [CAUP] and Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Portugal [FCUP]), A. Suárez Mascareño (Instituto de Astrofísica de Canarias, Tenerife, Spain [IAC], Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain [IAC-ULL]), P. Figueira (European Southern Observatory, Santiago, Chile [ESO-Chile], IA-Porto), A. M. Silva (IA-Porto, FCUP) M. Damasso (Osservatorio Astrofisico di Torino, Italy [INAF-Turin]), O. Demangeon (IA-Porto, FCUP), F. Pepe (Département d’astronomie de l’Université de Genève, Switzerland [UNIGE]), N. C. Santos (IA-Porto, FCUP), R. Rebolo (Consejo Superior de Investigaciones Científicas, Madrid, Spain [CSIC], IAC-ULL, IAC), S. Cristiani (INAF – Osservatorio Astronomico di Trieste, Italy [OATS]), V. Adibekyan (IA-Porto), Y. Alibert (Physics Institute of University of Bern, Switzerland), R. Allart (Department of Physics, and Institute for Research on Exoplanets, Université de Montréal,Canada, UNIGE), S. C. C. Barros (IA-Porto, FCUP), A. Cabral (Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Portugal [IA-Lisboa], Faculdade de Ciências da Universidade de Lisboa, Portugal [FCUL]), V. D’Odorico (OATS, Institute for Fundamental Physics of the Universe, Trieste, Italy [IFPU], Scuola Normale Superiore, Pisa, Italy) P. Di Marcantonio (OATS), X. Dumusque (UNIGE), D. Ehrenreich (UNIGE), J. I. González Hernández (IAC-ULL, IAC), N. Hara (UNIGE), J. Lillo-Box (Centro de Astrobiología (CAB, CSIC-INTA), Depto. de Astrofísica, Madrid, Spain), G. Lo Curto (European Southern Observatory, Garching bei München, Germany [ESO], ESO-Chile) C. Lovis (UNIGE), C. J. A. P. Martins (IA-Porto, Centro de Astrofísica da Universidade do Porto, Portugal), D. Mégevand (UNIGE), A. Mehner (ESO-Chile), G. Micela (INAF – Osservatorio Astronomico di Palermo, Italy), P. Molaro (OATS), IFPU), N. J. Nunes (IA-Lisboa), E. Pallé (IAC, IAC-ULL), E. Poretti (INAF – Osservatorio Astronomico di Brera, Merate, Italy ), S. G. Sousa (IA-Porto, FCUP), A. Sozzetti (INAF-Turin), H. Tabernero (Centro de Astrobiología, Madrid, Spain [CSIC-INTA]), S. Udry (UNIGE), and M. R. Zapatero Osorio (CSIC-INTA).

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration in astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates APEX and ALMA on Chajnantor, two facilities that observe the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society. 


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João Faria
Instituto de Astrofisica e Ciências do Espaço, Faculdade de Ciências, Universidade do Porto
Porto, Portugal
Tel: +351 226 089 855

Pedro Figueira
ESO and Instituto de Astrofísica e Ciências do Espaço
Santiago, Chile
Tel: +56 2 2463 3074

Nuno Santos
Instituto de Astrofisica e Ciências do Espaço, Faculdade de Ciências, Universidade do Porto
Porto, Portugal

Mario Damasso
INAF – Osservatorio Astrofisico di Torino
Turin, Italy
Tel: +39 339 1816786

Alejandro Suárez Mascareño
Instituto de Astrofísica de Canarias
Tenerife, Spain
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We have had the technology to launch an affordable robot interstellar mission since the 1950s.

In the wake of the Hiroshima and Nagasaki nuclear bombs, the Manhattan Scientists were keen to find peaceful uses for nuclear bomb technology. One of their ideas was Project Orion, using nuclear bombs to propel a spaceship.

Their most impressive hypothetical design, using H-Bombs, was just good enough to power a starship (link – search for the term “momentum limited”).

Project Orion focussed on designs which could carry humans. But what if instead of a large spaceship designed to limit acceleration to human tolerance, you built a disintegrating Chinese firecracker of a ship, with an acceleration hardened payload which could take a level of thrust which would turn human astronauts into jelly?

Maybe, just maybe we could take a close look at our nearest neighbour, and figure out if it was worth a second visit.

Update (EW): Renowned physicist Freeman Dyson was one of the lead scientists on Project Orion. Dyson calculated Project Orion had a theoretical top speed of 0.033C, fast enough to reach Proxima Centauri in 133 years, not thousands of years.

Update2 (EW): A few people have mentioned the difficulty of getting a signal back from 4 light years. According to the National Radio Astronomy Observatory, you would need a minimum 1MW radio signal to reach Earth from Proxima. A powerful radio, but not completely beyond imagination. If all else fails, the probe could announce “I made it” by saving a nuclear bomb and using it to power a nuclear pumped laser, a device developed during the Reagan Star Wars program. The US military won’t say how powerful the beam from a nuclear pumped laser is, but I’m guessing its more than a megawatt.

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Tom Halla
February 12, 2022 2:08 pm

There is the ”Far Centaurus” problem, in that any probe launched in the near future would take hundreds of years, and technology should improve enough so the probe is passed by a later probe.

Reply to  Eric Worrall
February 12, 2022 5:16 pm

If given objects and entities are supposedly addressed as should be, one way or another, either in relation or not,
basically by means of motion and distances and radius,
how then any conclusion reached (even about mass) is served as matter of fact via weight!?

Reply to  Eric Worrall
February 12, 2022 9:57 pm

Perhaps, you have got the “narrative” wrong… just perhaps.

“At just a quarter of Earth’s mass, the planet is also one of the lightest exoplanets ever found.”

That I think maybe the supposed line that must be burned into your brains, I think.
And not the FTL or other as such smart thoughts.

Oh well,do not mind me… Eric.


Reply to  whiten
February 13, 2022 10:07 am

Ok, dear Eric!
Have you or not the ability to understand, what the adding of the “rogue” to a “ghost” mean. in reality, Eric!

It still happens to be an Australian…thingy!


Reply to  whiten
February 13, 2022 10:08 am

This is not a joke… Eric!

Reply to  Eric Worrall
February 12, 2022 5:57 pm

Mmm. The “Trek” style warp drive is currently considered possible, if completely impractical.

Let us hope that the show is not equally prophetic about our encountering a “V’Ger” – I’m not sure that we could force such a thing into suicide with Kirk’s logic.

Reply to  Tom Halla
February 12, 2022 3:26 pm

There is a chance that the technology will improve like that. There’s also a chance that it won’t.

Gary Pearse
Reply to  MarkW
February 12, 2022 4:29 pm

They’ve got a lot of asterisked PhD physicist folk over the past few decades to get cleared out and may need replacement universities with a high standards re-established to undertake the work of improving technology for an alpha Centauri trip. (Rehab of the formerly top unies is likely not possible )

Rick C
Reply to  Eric Worrall
February 12, 2022 7:08 pm

133 years at 0.033 speed of light may seem doable, but your probe would be traveling at 22 million miles per hour when it wizzes by Alpha Century unless you use a bunch more nuclear bombs to slow it down and double the time of the trip. Do you really think the cost which would surely be in the trillions would be worth it to a human population who will be long gone before they could ever know if it worked? We’re going to need that money to rebuild our reliable energy 8nfrastructure in a few years once the greenies are done wrecking it.

Reply to  Eric Worrall
February 15, 2022 1:31 pm

What about a nuclear salt water reactor, check it out on youtube

Reply to  Tom Halla
February 12, 2022 3:36 pm

Not if Americans keep voting for left wing idiots…

Reply to  Tom Halla
February 13, 2022 7:40 am

Dr. Zefram Cochrane is eagerly awaited.

Until then, we’ll still be launching sailboats.

February 12, 2022 2:11 pm

What we’d see there if arrived today =

Gary Pearse
Reply to  gringojay
February 12, 2022 4:33 pm

This may be what the graduation exercises at Harvard will look like.

February 12, 2022 2:15 pm

When will we do a near-field inspection to confirm our inference and assertion of signal fidelity and model fitness.

Jeff Norman
February 12, 2022 2:18 pm

What would they see if they pointed the James Webb Space Telescope at it?

Proxima Centauri is a red dwarf, more active than Trappist-1.

February 12, 2022 2:26 pm

“My question – when are we going to send a probe to take a look?“

When someone invents FTL or a way to fold space-time

Reply to  Eric Worrall
February 12, 2022 2:32 pm

With FTL it would take 2 or 3 years

Artificial Gravity would be a welcome addition!

Reply to  Eric Worrall
February 12, 2022 5:31 pm

You can already buy FTL for 9,99€… in Internet.


Reply to  whiten
February 12, 2022 10:36 pm

You can also buy a number of cold energy fusion reactors and a few bridges and islands.

Reply to  fretslider
February 12, 2022 6:34 pm

I question your numbers. If the star is 4 light years away, then the speed of the starship would have to be twice the speed of light. How do you propose to do that with present technology?

Eric Worrall’s numbers are much more realistic.

Next question is how much time deceleration will take so that the probe does not overshoot the star.

Reply to  DonK31
February 13, 2022 7:15 am

Who said anything aboutFTL being present technology?

Alan Robertson
Reply to  fretslider
February 12, 2022 5:15 pm

In the mean time, for a mere $75 (US), anyone can apply for a one- way trip to colonize Mars, via this Century’s P.T.Barnum plan.
Maybe they should practice terraforming the Mojave Desert, while they wait for liftoff.

Alan Robertson
Reply to  Eric Worrall
February 12, 2022 6:11 pm

An often overlooked benefit of melting glaciers/rising sea levels is, increased atmospheric moisture, producing more rain in places that need it.
The Sahara was a savannah, before some catastrophic event started a glaciation era, locking up water as ice and eventually dooming the Ancient Egyptian civilization.

The ongoing greening of the planet, likely owes more to increased rainfall, than rising CO2.
History clearly details how civilizations have flourished during warm periods.
There’s a reason for that; crop yields increase, with adequate water for optimal growth.

Reply to  Alan Robertson
February 13, 2022 7:25 am

When the Sahara was last green, we were coming out of the last glacial cycle. World’s temperatures and sea levels were lower than they are today.

February 12, 2022 2:34 pm

A quarter the size of Earth, orbiting between the star and habital zone. As active as red dwarfs are, it’s most likely a burned out cinder.

Reply to  Eric Worrall
February 12, 2022 2:54 pm

Common sense would dictate that we go as late as possible and as prepared as possible

Reply to  Eric Worrall
February 12, 2022 3:31 pm

If it’s lost the atmosphere, it’s lost any ocean it may once have had.

Reply to  Eric Worrall
February 13, 2022 7:27 am

For an ocean to be thousands of miles deep, the planet would have to be many times larger than the earth. This planet, according to the article, is only 1/4th the mass of the earth.

Robert Alfred Taylor
Reply to  Eric Worrall
February 12, 2022 7:33 pm

White dwarfs are racists who devour their children.
Anton Petrov: First Discovery of a White Dwarf Actively Consuming an Ancient Planet

February 12, 2022 3:26 pm

We’ve already sent inter-stellar probes but they will take 40,000 years to get there. link They will likely be passed by later probes.

Reply to  commieBob
February 12, 2022 4:01 pm

A probe hasn’t been sent that direction. The page just references a statement that if one of the existing probes was aimed towards Alpha Centauri, it would take 40,000 years to get there.

Gary Pearse
February 12, 2022 3:41 pm

4 million km from the star, with a 11 day year! And this is a candidate for living things? I hope there is a thick ozone layer on it I may refuse to go.

Reply to  Gary Pearse
February 13, 2022 7:29 am

It’s orbiting a red dwarf which is many times dimmer than our star.

February 12, 2022 3:41 pm

The Intergalactic Council forbids approaching an orbiting body with detectable intelligent life forms closer than 1 million light years.

Reply to  pochas94
February 12, 2022 11:12 pm

The whole galaxy is only ~120,000 light-years wide, we wouldn’t be able to even leave our own planet with a “Hitchhiker’s Guide to the Galaxy” level of silly law like that.

February 12, 2022 3:56 pm

When are we going to send a probe to take a look? Are you kidding?

Proxima Centauri is only 4.246 light years away.

Proxima Centauri is 4.2 light-years from Earth, a distance that would take about 6,300 years to travel using current technology.

Even if a probe took a transmitter strong enough to send a signal back to Earth, the message would take another 5 years or so to return… make it an even 6,305 years.

If we are in a hurry, better get the probe on its way!

Reply to  Eric Worrall
February 12, 2022 6:51 pm

Eric ==> Project Orion has a hypothetical top speed of “0.03 C and possibly faster”.   1950s Science Fiction was full of hyper-lightspeed vessels. We do not have any even near-lightspeed vessels operational or any in-use technology that can be expected to achieve such speeds.

NASA Probe, Fastest Object Built by Humans, Passes Sun at Record-Breaking 364,621 mph. NASA’s Parker Solar probe smashed its own speed record, accelerating to a velocity as great as 101 miles per second, or more than 364,000 miles per hour, as it loops the sun.”

The speed of light is approx 186,000 miles/second. Nothing we have will be going to Proxima Centauri any time — not even in any near-far-distant time.

Reply to  Eric Worrall
February 12, 2022 10:39 pm

What Dyson was referencing is well covered

Reply to  Eric Worrall
February 13, 2022 1:41 pm

Eric ==> Gee, so easy a baby could do it! You’d think that we’d be all zipping around the galaxy by now, eh?

Course, I’m still waiting cor my flying car, my freezer-sized home nuclear power plant, a trip up to the stars in my space elevator…..

Wishes just ain’t fishes!

Reply to  Eric Worrall
February 15, 2022 7:13 am

Eric ==> Several friends and family are pilots — and the problem they present is this: If flying for flying’s sake is not enough for you, you’ve wasted your time and money. The one exception is if flying is just a quick (or only) way to get where you’re going.

Some have found a solution to the airstrip problem by flying float planes and having home and destinations on the water. Not unusual in my part of the country to find a float plane docked at a marina.

Reply to  Eric Worrall
February 13, 2022 7:38 am

First off, that’s it’s initial speed, it will slow down a lot as it climbs out of the Sun’s gravity well. Yes it will speed back up again as it approaches the other star, but it will still spend most of the flight at a speed well below it’s initial speed.

Secondly, you still haven’t addressed the problems of sending a signal back. It’s taking everything we have to receive signals from Voyager, and galactically speaking it’s still on the same block.

Randle Dewees
February 12, 2022 4:11 pm

And while you are over there, pick up a copy of the plans for the hyperspace bypass that requires the destruction of Earth. Or is it Alpha Centauri, anyway, somewhere over there.

Earl Rodd
February 12, 2022 4:28 pm

I do think I know what we would find if sent such a probe. This is based on experience with our Solar System. As a kid, I read a lot about astronomy. I still have my books from the 50’s. The interesting part is how confident those books were about the composition and geology of all the planets using very indirect means of measurement. So what happened when spacecraft went out and had a much better look? Those confident, and reasonable, assertions based on indirect measurements were generally very, very wrong. So my prediction: a close look at whatever is orbiting this star will be nothing like what we expect. Maybe nothing and the exoplanets are an artifact of measurement. Maybe … who knows – that’s the point, we don’t know. Given how much further away this star is that even the outer planets, I don’t give us much chance of our current guesses being very close to reality.

Joseph Zorzin
February 12, 2022 4:58 pm

why send a probe when we have the James Webb Space Telescope?

Tom Abbott
Reply to  Joseph Zorzin
February 12, 2022 5:30 pm

And we can build much bigger telescopes than Webb.

Reply to  Tom Abbott
February 12, 2022 11:22 pm

The James Webb is not in the visual range, so no fun.

How huge of mirror would it take to image a planet around Proxima, say as good as Pioneer for starters?

Tom Abbott
Reply to  PCman999
February 13, 2022 4:55 am

In the case of space-based telescopes, we make a big mirror by separating a couple of large Webb-type telescopes by a large distance, and then combine the signals of both telescopes into one, when observing the same object, and that would give us the equivalent of a mirror as large as the separation between telescopes. How about a telescope with a virtual mirror the width of the Earth’s orbit. We ought to be able to see something new with that configuration.

Thomas Gasloli
February 12, 2022 4:58 pm

Dear Eric
You seem very keen with on this particular bit of space research, does that mean you are putting up the money?

J. R.
Reply to  Eric Worrall
February 12, 2022 8:26 pm

Stay away from GoFundMe, they’re not reliable.

Interested Observer
February 12, 2022 5:31 pm

How about we learn to walk before we embark upon that marathon? We’re still learning to crawl across our solar system so, maybe we should master that before we try to get to another star system. We haven’t even sent dedicated robotic missions to Uranus or Neptune yet. Let’s not get ahead of ourselves.

And then there’s the cost. How much would this mission to nowhere actually cost? Probably more than the many trillions of dollars it would cost to go plant some flags on Mars. At least that stupid idea has the merit of an actual outcome (flags on another planet); a mission to another star system, at this point, would likely have no outcome at all. Who wants to wait hundreds, or even thousands of years, to know whether the probe made it there? If it crashed into something unforeseen along the way, how would we even know?

Best to get back on the opium pipe and enjoy a few more dreams – until such time as warp or wormhole drives (or some other technology far beyond our current level) are invented.

Interested Observer
Reply to  Eric Worrall
February 12, 2022 9:36 pm

Uh, no.

“Developed” means having built and tested a working prototype (see: rail and coil guns – which were sci-fi not long ago but now have working prototypes). If that has happened, can you direct me to where this prototype currently resides?

I think you mean “Someone wrote some ideas down, did a bit of math and concluded it was technically feasible.” I must have slept through the testing of spaceships powered by nuclear explosions; I can’t recall when that happened.

Honestly, I’m more concerned that, given the current pace of exploration, I’ll be dead before we’ve sent missions to every major planet in our system. I really don’t care about some idea that won’t show a result for hundreds (or thousands) of years, if ever.

Craig from Oz
Reply to  Eric Worrall
February 13, 2022 7:22 pm

…Freeman Dyson’s son claimed Dyson senior even built and tested the small atom bombs…

And no body else noticed?

This claim seems… odd. I will give you that this short paragraph isn’t a lot to go off, but are we suggestion there was a programme to build atomic bombs being casually run by ‘not the military’ and they did actual tests?

And these tests are not common knowledge?

Like I said, this claim seems… odd.

Tom Abbott
February 12, 2022 5:34 pm

A laser-powered interstellar probe would be the best way to explore the nearest star to the Sun.

The article talks about slowing the laser-powered probe down as it reaches the Proxima Centauri system but it would be a lot easier to forget about slowing the probe down and just record data as the probe sails through the solar system.

Reply to  Tom Abbott
February 13, 2022 12:23 pm
Gordon A. Dressler
February 12, 2022 6:06 pm

In the above article, author Eric Worrall leads with this question:

“When are we going to send a probe to take a look?”

Simple question in response: since the Proxima Centauri system is about 4.25 light-years aways from Earth, has anyone done a basic calculation to know the antenna size (aperture) and transmitter power necessary to send a radio signal, at “reasonable” minimum data rate (say, >100 bits/sec), when it reaches Earth from being transmitted at the distance of the Proxima Centauri system?

Even though large radio antennas and signal amplification/processing like that employed at the NASA Goldstone Deep Space Communications Complex in California can detect RF signals at picowatt levels (IIRC), I suspect to send such power levels to Earth from Proxima Centauri would still require a multi-megawatt RF transmitter. This would not be something that could be included on a lightweight probe sent to that star system.

As a separate issue, optimistically assuming a probe (of any arbitrary mass) could be sent out from Earth with a coasting velocity of 0.1% that of light (186 miles/sec, or about 300 km/s, which is about six times faster than the highest velocity comets ever observed entering the solar system) toward the Proxima Centauri system, it would take about 4,250 years to get data back from that super-high-speed spacecraft.

Does anyone really want to wait that long for a “return on investment”?

Gordon A. Dressler
Reply to  Eric Worrall
February 13, 2022 8:41 am

My understanding is that Project Orion no longer remains remains theoretically feasible.

I have read previously that detailed engineering analysis of the concept has pretty much shown that nuclear explosion-driven propulsion in space won’t work because, absent an ambient atmosphere, almost all the explosion’s energy directed toward the spaceship “driver plate” would hit it as high energy x-rays and gamma-rays, which have both extremely low total momentum and relatively low interaction cross-sections with solid matter, even lead. That is, assuming the driver plate is made of pure lead, or even depleted uranium, (ouch! for spacecraft mass) it would difficult to ablate away a thin layer at high “exhaust” velocity (= decent specific impulse) for efficient thrust as opposed to just heating most of the driver plate mass below its boiling point.

In simple terms, a fission device or fusion device exploded in the vacuum of space DOES NOT produce the blast wave that people normally associate with such explosions within earth’s atmosphere.

Encasing the nuclear device itself in a material that will vaporize to produce a blast wave against the spacecraft pusher plate is extremely inefficient given that the explosion cannot be so close to the pusher plate as to destroy it via its intense X-ray and gamma ray radiation, not to mention the frequency of nuclear explosions needed in the Orion propulsion concept.

Craig from Oz
Reply to  Gordon A. Dressler
February 13, 2022 7:36 pm

In simple terms, a fission device or fusion device exploded in the vacuum of space DOES NOT produce the blast wave that people normally associate with such explosions within earth’s atmosphere.

It can if you remaster the originals with a more up to date special effects team.

Then you can get blast discs in a single flat plane!

Also Han Shot Second… or something… Science!

Gordon A. Dressler
Reply to  Eric Worrall
February 14, 2022 12:58 pm

Eric, you are perfectly welcome to do so.

I will just give a parting comment that any “pusher plate” receiving particulate matter (i.e., tungsten “shaped charge” debris) impacts at velocities of up to 15,000 km/s will not structurally survive more than10 such blasts no matter what it is comprised of (excluding, of course, unobtainium), with the result that any such debris thence passing through the perforated/broken apart pusher plate will then destroy the spacecraft ahead of it.

J. R.
Reply to  Gordon A. Dressler
February 12, 2022 8:43 pm

Perhaps, after launching the probe, we could place a series of repeaters in space between here and Alpha Centauri. Maybe that would do the trick.

Gordon A. Dressler
Reply to  Eric Worrall
February 13, 2022 9:00 am

Ummmm . . . the useful life of fuel rods in current operational nuclear reactors is about six years. I’m not sure what their useful life would be in a reactor that is in idle mode, but I doubt they would still be useable after sitting idle (outside the reactor core but still in close proximity to one another) for 133 years, yet alone for 4,250 years or more.

Crispin Pemberton-Pigott
February 12, 2022 9:23 pm

Why not take one of the captured or replica alien ships and check the place out? For such a journey it must be possible to work out a way of keeping people alive. Those craft seem to be able to accelerate rapidly and indefinitely.

February 12, 2022 10:06 pm

One bit of data every 133 (+4 for the return signal) years? I’ll do it! I’m in!

David Blenkinsop
February 12, 2022 11:03 pm

As intriguing as it may be to think of getting a probe up close to the nearest star system, what human institution is going to invest in a 130 year mission, and who is going to get excited about waiting around for that?

Maybe a really humungous lunar telescope would be more likely, as in a ‘scope so good you could map the surface of ET planets, even out to say, a hundred light years?

Interested Observer
Reply to  David Blenkinsop
February 13, 2022 1:55 am

If a base on the Moon was going to be built, a giant telescope would be one of the best reasons for doing it.

Gordon A. Dressler
Reply to  Interested Observer
February 13, 2022 10:25 am

Even if would could (actually, we can’t) build a steerable optical telescope of sufficient diffraction-limited optical surface aperture to resolve surface details out to, say, 100 AU, or about 10 times the distance between the Sun and Neptune’s average orbital distance, it would face insurmountable problems such as being stabilized against long-lasting moonquake vibrations ( ) and lunar-monthly day/night temperature variations on its far side.

Note that the Moon is tidally locked with Earth so that only its “near side” continuously faces Earth, but that doesn’t mean that its so-called “dark side” never sees sunlight nor that its farside is continually facing a fixed direction into deep space.

And the distance to Proxima Centauri is about 270,000 AU from Earth.

Forget about ever optically imagining, from near-Earth, objects that are at the distance of Proxima Centauri.

David Blenkinsop
Reply to  Gordon A. Dressler
February 13, 2022 5:55 pm

If you go to,
an astronomer, Loren Petrich, posting there suggests that a free flying space telescope with an effective aperture of 380 *kilometers* could begin to get some imaging detail on Alpha Centauri planets.

What I notice is that this is not so large an aperture as to discourage the use of what’s called Astronomical Interferometer imaging or Aperature Synthesis imaging to get that effective aperture from multiple telescopes. Such multiple elements could be on the lunar surface, even, with no reason why that couldn’t be a steerable aperture either. Assuming that this can be worked out, notice that the moon actually has a diameter of *3400* km. So, there you have a nice solid surface with essentially no atmosphere getting in the way, and with the ‘moonquakes’ possibly being something that the technology could compensate for? I mean, in your article reference, if the Moon sometimes ‘rings like a bell’ for 10 minutes, it is at least quiet most of the time, right?

To me, this sounds like a possibility for seeing quite a lot in the vicinity of nearby stars, though likely not the resolution we’d be hoping for from a space probe.

Gordon A. Dressler
Reply to  David Blenkinsop
February 14, 2022 2:51 pm

I duly note:
1) reference to an article posted on,
2) reference to an astronomer (not an optical imagining engineer),
3) the phrase “could begin to get some imaging detail on Alpha Centauri planets”.

Besides the above, anyone who has ever tried to take optical pictures at low shutter speeds—and we would be talking of “shutter” speeds of tens, if not hundreds of hours for the postulated synthetic aperture telescope on the Moon—knows that the camera needs to accurately track the moving object to keep it stable relative to the camera’s field-of-view to avoid relative-motion-induced-blur. Since any planets orbiting Alpha Centauri-C/Proxima Centauri (closer to us than Alpha Centauri A/B) would necessarily be in orbital motion relative to their central star, the camera would need to know exactly where the planet is positioned and in what 3-dimensional direction it was moving and how fast—its complete orbital ephemeris, as it were—before it could be imaged clearly.

Perhaps you can appreciate the chicken-and-egg problem here: before we can accurately image a moving planet at 4.25 light-years distance (assuming that is even remotely possible) we have to establish the orbital ephemeris of the planet, but to accurately establish a planet’s orbital ephemeris, we first need to accurately image it’s position and movement in space.

Details, details, details.

David Blenkinsop
Reply to  Gordon A. Dressler
February 14, 2022 9:27 pm

So, in your “chicken and egg” problem, imaging a planet is defeated by what you seem to suggest is a paradox of sorts? Can’t image a planet closely enough because we can’t ever track it closely enough?

More generally, synthetic aperture — combining different telescopes for a much bigger effective aperture — is a pretty new thing, at least for optical frequencies, although it *is* very well established for use in radio telescopes. Whatever is or isn’t possible with this, it at least doesn’t require more than a hundred years just to get there, anyway.

February 13, 2022 2:22 am

Constant acceleration at one G (ravity) could see an “Explorer” space craft achieve half the speed of light or 92,000 miles per second by the halfway point between Proxima Centauri & Earth. At that point “Explorer” would turn 180 degrees & point its engines at Proxima Centauri & begin to slow down in order to go into orbit. I have no idea what fuel source would be necessary to power this vessel or what the elapsed time would be for any inhabitants (18, 30 or 50 years), but on Earth, perhaps 150 years would have passed. During those 150 years, there will have been so many advances that when “Explorer” arrives at its destination, humans could be there to welcome it, although I doubt it. Leaving Earth for the stars means never returning within many lifetimes on Earth, which is why space cowboy entertainment for the untutored are anathema to me. OTOH, a Stargate to fold time & distance? If only?

Intelligent Dasein
February 13, 2022 4:38 am

Please, no more guest posts by Eric Worrall. This is an absurd waste of time.

Tom Abbott
Reply to  Intelligent Dasein
February 13, 2022 5:05 am

I didn’t find it to be a waste of time. It’s an interesting subject.

James Donald Bailey
February 13, 2022 7:03 am

A theoretical writeup is not technology.

This is a big problem with “Believing Science”. An awful lot of technology has to be invented to use “existing technology” that way. And lots of times these writeups are pollyannish in that they don’t really look hard at the problems.

Similarly, we have spent huge fortunes on existing technologies of wind and solar energy. Lots of pollyannish writeups were used to goad governments into destructive actions.

BTW there were lots of ‘wonderful uses’ of nuclear technologies. Nuclear airplanes and space exploration. We even hoisted a reactor up high to conduct tests.

DOE’s secluded site has unusual history – Atomic City Underground (

First airborne nuclear reactor | Guinness World Records

Somehow, none of these ‘wonderful’ ‘existing technologies’ panned out. But with launch catastrophes, crashes on take-off and Sky Lab crashing to earth, it would just be a matter of time before we would have such a catastrophe with an air or space borne reactor.

And as others have pointed out, Stuff like this has to happen in the working life of the involved scientists. 20-30 years for the trip with a 4 year delay in receiving the results of a 10 year exploration program. A 30 year old junior scientist at launch would be 64-74 years old Senior on the project at its conclusion.

John Bell
February 13, 2022 8:50 am

It would take a year to accelerate to light speed at one G, travel at that speed for 2 years and then another year to decelerate to a stop at one G.

Gordon A. Dressler
Reply to  John Bell
February 14, 2022 2:59 pm

To accelerate ANYTHING to asymptotically-near light speed at a constant acceleration of 1 g, would require asymptotically-near infinite thrust due to the Einstein-defined laws coupling relativistic mass-increase as a function of increasing relativistic speed.

Alan Watt, Climate Denialist Level 7
February 13, 2022 11:09 am

Dyson calculated Project Orion had a theoretical top speed of 0.033Cfast enough to reach Proxima Centauri in 133 years, not thousands of years.

Plus 4 years or so for any kind of signal to get back to us. Considering civilization will have been destroyed 13 times over by climate change and we will be well into the 7th or 8th great mass extinction by then, I don’t think anyone will be around to understand or care.

Why not send one of the 8 alien spaceships we’ve been studying at Area 51 for the past 30 years? They should be able to make the trip out to Proxima Centauri and back before Greta is old enough to drink.

Gordon A. Dressler
Reply to  Alan Watt, Climate Denialist Level 7
February 14, 2022 3:03 pm

Ummmm . . . has having 8 alien spaceships to study, instead of just one, meant that human understanding of this alien technology has gone eight times faster?

Inquiring minds want to know. 🙂

February 13, 2022 12:19 pm

“when are we going to send a probe to take a look?”
circa 2040. Starshot Breakthrough –
is developing laser-launched gram-massed lightsail craft for exploring the Proxima Centauri system. The current plan is to launch several thousand probes over the course of a few months, accelerating the probes to approximately 0.2 c. The probes would form clusters and send data back using optical transmission techniques. They would fly through the system and return images and basic environmental data.

we’re looking to develop precursor missions in the next decade for looking at Potentially Hazardous Asteroids and OORT cloud objects.

The full Proxima Centauri mission would require a GW class laser array, with the sails requiring atomic-scale fabrication. The precursor missions can be accomplished with MW class industrial lasers and micrometer scale 3D printing.

Gordon A. Dressler
Reply to  Paul Blase
February 14, 2022 3:06 pm

Was the pitch for funding accidentally dropped, or did the WUWT moderators do their job?

Gordon A. Dressler
Reply to  Gordon A. Dressler
February 14, 2022 4:26 pm

Gordon A. Dressler
Reply to  Paul Blase
February 14, 2022 4:28 pm

Couple your “gram-massed lightsail craft for exploring the Proxima Centauri system” with Eric Worrall’s previously posted comment above that “You’d need a 1MW signal to reach Earth, according to NRAO. A small nuclear reactor could supply the power. It wouldn’t hurt to have a repeating station on the outer edge of the solar system, or possibly another one further out.” and you might just see a slight issue that needs to be fleshed out prior to “circa 2040“.

Anyway, thanks for today’s comedy posting, very enjoyable.

February 13, 2022 2:11 pm

A Red Dwarf that is known to have powerful frequent flares. Not the best candidate for finding life on one of it’s planets I would think.

February 13, 2022 4:18 pm

It always amazes me how many astronomers get paid significant bucks per annum for pursuing a hobby.

February 13, 2022 6:03 pm

A constant 1 g acceleration spacecraft would take 5 years ships time, allowing for deceleration.

A hydrogen fusion engine would need something like 330 thousand tons of fuel for a 100 ton spacecraft.

An anti matter engine would cut fuel requirements to about 3 thousand tons.

Tom Schaefer
February 14, 2022 9:23 am

Let’s make the investment in first, so the people that launch it get to see the return data.

Jørgen F.
February 15, 2022 12:27 pm

When did we stop doing projects that lasted more than a lifetime to complete – and have our civilisation been declining ever since?

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