What is the Closest Earth-like Exoplanet?

Possible Exoplanet View of M dwarf Parent Star

Recently I was asked this question by a friend which made me stop and ponder it for a minute. Of course, my mind jumped to my older posts on what an 'Earth-like' planet is along with the definition of a "habitable" planet (the key differentiator being Earth-like doesn't necessarily mean habitable or terrestrial).

So this isn't an easy question to answer since we don't fully understand what habitable or terrestrial might look like for different exoplanet stellar systems. For example, if we're going to limit the question to exoplanets around F, G, K and M dwarf stars due to stellar lifespan (for example, bright A5V stars only have a lifespan of about 750 million years), then one current estimate is there are 65 billion terrestrial planets around these 4 classes of stars in the Milky Way galaxy. However, since cool, low mass M dwarf stars comprise 76% of the total, terrestrial exoplanets are going to be in tight, short orbits, most likely tidally locked with low UV stellar radiation. That doesn't rule out Earth-like habitable exoplanets, but that's a large unknown at this point (something we'll talk about in a future post). 

So, to get back to the question, let's pick F, G and K main sequence stars first. Using that criteria, 82 Eridani in Eridanus (visible from the southern hemisphere) is going to be the best answer for those stellar candidates. At about 20 light years away, the two planets, 82 Eridani e and f orbit a G6V star (very similar to the Sun) with a periods of 147 and 647 days potentially within the star's habitable zone. As of this writing, both fall on the edges of that habitability zone with e on in the inner edge and f on the outer edge. Also, the detected exoplanets masses are at least 4x that of Earth's. Given that, this is probably the best case for now. 

In the northern hemisphere, if you look in the constellation of Cassiopeia, the orange star Gliese 892 (stellar type K3V - cooler than the Sun) may be the closest at 21 light years. However, the main problem is the candidate exoplanet's mass at over 10x Earth's. Also, that particular exoplanet hasn't been confirmed.

Honestly, there's not much beyond this since we're dealing with more distant, brighter stars (see my mention of the Malmquist bias in my previous post). If we go back to lower mass, cooler M dwarf stars then my favorite pick is Gliese 667 in the constellation of Scorpius at 23 light years away. It is a triple star system with the third star, Gliese 667 C, having detected exoplanets. Planet e with an orbit of about 62 days and mass of about 3x that of Earth's is within the star's habitable zone. There are many other M dwarf star systems with detected exoplanets. If you're interested, you can browse the Habitable Worlds Catalog or NASA's Exoplanet Catalog to see what potential exoplanets could be candidates.

Given how difficult this question is, there just isn't a good answer yet. There are still so many assumptions along with unanswered questions as to just what extraterrestrial life is, how it may evolve and what types of stellar systems would support it. All we can do is continue to gather more data and assume life on Earth as the initial standard to measure against.

The New SETI Protocols for Discovery of Alien Life

Imagining the SETI Announcement

If you were a scientist who just happened to discover and verify the existence of extraterrestrial life, how would you proceed to announce it? What would be your proper course of action? This was the question asked by SETI scientists in the 1980s when they began to ponder how a discovery like this might unfold. By 1989 they had drafted what was called Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence, or, the First SETI Protocol (you can read it here). It was revised and renamed in 2010. 

So, now, in 2026 another revision is on the docket to be voted on by the members of the Permanent SETI Committee which is much more robust than previous versions. With the advent of social media along with more public mistrust in information, the authors have hinted at their reasons for the change: 

 

to prepare an updated version of the 2010 Declaration of Principles Concerning the Conduct of the Search for Extraterrestrial Intelligence, with the aim of preserving the enduring values of earlier documents while making them relevant to the realities of twenty-first century science, media, and public engagement. 

Having worked in industry for many years, I understand the need for protocols and processes. However, I’m not convinced that discoveries of extraterrestrials be it from SETI scientists or aliens announcing themselves publicly is going to follow the declaration’s standards. It seems that extraterrestrials and first contact may be a messy social event no matter what kinds of best practices we as humans develop. Take this statement for example:



 

SETI practitioners shall adhere to the highest ethical standards, ensuring cooperation, honesty, and integrity in all aspects of their work. They will collaborate with international legal authorities to establish clear frameworks for managing the dissemination of information about potential extraterrestrial detections and comply with relevant laws and regulations.

When dealing with an event of worldwide importance, adhering to the standards outlined are hard to imagine for something that could be this messy and chaotic. Nevertheless, it’s good to have a set of principles to drive awareness in the scientific community.

You can find the new revision in the proposal paper here.

The Eschatian End to an Extraterrestrial Civilization

If you’re familiar with Dr David Kipping of Columbia University you may have seen his appearances on various YouTube channels or his Cool Worlds channel talking about extraterrestrial life. Kipping recently published a very short paper hypothesizing how we might first detect an extraterrestrial civilization based on observational bias. But, before we get into that let’s first pronounce the new word derived by Kipping - eschatian (es-ska-ti-un) derived from the word eschatology (es-ska-ta-le-gee)^[1] meaning the final events in the world or history. Typically eschatological discussions are reserved for Christian theology but the word does serve some purpose to what some may coin “end times”.

So how does that definition tie to extraterrestrials? Kipping hypothesizes that our first detection of signals may be very similar to other types of large and loud events in then universe (think supernovae explosions, gamma-ray bursts, etc) or objects that emits large amounts of energy that can be detected. Add to that astronomers are burdened with something called the Malmquist bias meaning we detect the brightest, most energetic objects first and lower energy objects are hidden until more sensitive technology is developed.

Given those conditions our first detections of any extraterrestrial civilization may very well be its end - the “loud” burst of energy from a nuclear war or some other catastrophic event. As Kipping notes 

 

rare examples of loud civilizations will truly be more likely to be detected, against the backdrop of what is (presumably) a more abundant quiescent population.

 

He goes on to create a simple toy mathematical model based on the fraction of loud and quiet civilizations and their possible time windows of extreme energy output from an event. In his discussion, the suggestion is some wide field observations may be able to detect such transient events.

This is an interesting hypothesis that touches Level 2 of the exoastronomy categorization. Granted, this is highly speculative without actual values to use for the model. However, these are the types of scientific speculations we need to see more of. His paper can be found here. (I may do a deeper dive on the model in a later post)

1. Note that I'm not using standard dictionary pronunciation guides here↩

Washington Post Skeptic Op-Ed on UAPs

NASA UAP Study Committee

Recently, the Washington Post ran an editorial speculating about the origin and beliefs surrounding UAPs. If you’ve looked at my categorical breakdown of how to classify any information regarding UFOs or UAPs, you’ll see this clearly falls under my lowest Level 4, or, non-verifiable conjecture or opinion (see the definitions of levels here). Now, you might disagree with me and the author based on all of the testimonial evidence provided by government hearings. But, Mr. Shermer is espousing his own opinion on the matter as a contributor to Skeptic Magazine.

As usual, even the small additions of wording like “tinfoil-hat-wearing kooks” (even when written in the negative as “not kooks”) and “Bart Simpson balloon” still pushes the public stigma against positive and constructive conversations regarding the phenomena. Those types of small stereotypes printed in the negative do not help with modifying the conversation towards positive, scientific and cultural discussions.

The real meat of my disagreement comes in the punch line “could UAPs really be space aliens?” And, as usual, the extraterrestrial hypothesis is thrown under the bus with the tired old skeptic standard - distances between stars is too far, grainy photographs, etc. What’s interesting is why I consider this a Level 4 analysis in my rating system. The answer is that it is just as easy to post a similar op-ed with a different viewpoint using the identical argument. In fact, the entire article could be exactly the same except for the last 2 paragraphs that focus on religious-like beliefs due to declining religiosity. These could be rewritten to emphasize stronger evidential analysis while compiling scientific evidence (moving the conversation to Level 3).

If you’ve read this far you probably think I’m in complete disagreement with his opinion. I’m not. It’s more about the tone of the discussion and where we need to focus on both rational and scientific investigation without throwing the old stones (that I’ve been seeing since the 1960s).

Webb on the Forefront of Earth-like Exoplanet Discoveries

After analyzing data from NASA's Transiting Exoplanet Survey Satellite (TESS), the research team led by Kevin Stevenson and Jacob Lustig-Yaeger from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland chose to observe the exoplanet LHS 475 b using the NASA/ESA/CSA James Webb Space Telescope. With only two transit observations, Webb's Near-Infrared Spectrograph (NIRSpec) captured the planet and confirmed its existence.

LHS 475 b is 41 light years away with a radius nearly equal to that of Earth and an orbital period of two days around an M-type (M3.5V) star in the southern hemisphere constellation of Octans. While the observation couldn't fully identify what atmosphere is present on the planet, it isn't a thick methane-dominated atmosphere. But, there is a possible carbon dioxide atmosphere, which is contrary to expectations due to its compact nature. Further observations with more precise measurements are being planned for this summer in order to distinguish between a pure carbon dioxide atmosphere and no atmosphere at all.

Clearly we're on the cusp of some significant exoplanet discoveries!

You can read more here 

Swarming for Extraterrestrials

Interesting idea out of NASA's Innovative Advanced Concepts (NIAC) - a robotics engineer has been awarded Phase II funding for miniaturized micro-swimmers that could be deployed through an ice probe beneath the ice surfaces of Europa or Enceladus. The swarm of swimming robots only inches in dimensions could explore ice-covered ocean worlds much faster than individual robotic missions when searching for signs of life.

Mars Atmospheric Pressure affecting Ingenuity

Seasonal pressure variation on Mars

A very interesting update on the Mars 2020 mission appeared recently - specifically the Ingenuity helicopter's ability to fly in relationship to Mars' atmospheric pressure. The atmospheric density of Jezero crater is dropping. 

Seasonally, the atmospheric pressure on Mars varies approximates 25-30% peak-to-peak (Smith 2008) due to the exchange of CO2 with the polar ice cap. Ingenuity was designed for flights in atmospheric densities of 1.2-1.5% of Earth's. However, the density may drop to 1.0% requiring some extra spin-up of the blades to stop any aerodynamic stalling.

This does imply some considerations on how atmospheric variability might affect habitability when deeper exoplanet data is analyzed (Linsenmeier et al. 2015 have a good overview)

You can read more about the Ingenuity issues here.

Avi Loeb Continues to Push the Science of ET

Oumuamua - Credit ESO M. Kornmesser

It's great to see a respected Harvard scientist push the envelope on extraterrestrial life. Avi Loeb was chastised for his speculation on Oumuamua but has bounced back with backing for his Galileo Project - "the search for extraterrestrial technological signatures of Extraterrestrial Technological Civilizations (ETCs) from accidental or anecdotal observations".

 

Loeb published an interesting op ed in Scientific American yesterday outlining his opinions on AI-enabled self-replicating technologies exploring the galaxy and how we might be able to detect these extraterrestrial objects. It's a short read but demonstrates the core idea of his project.

 

Loeb is no lightweight here and has published a number of scientific papers (one example Lingam & Loeb 2019) working through the problems of alien panspermia, probabilities of encounters and implications of the galactic environments on extraterrestrial life.