Is the Grass Greener on Exoplanets?

Avi Loeb
5 min readApr 2, 2024


Art inspired by the interstellar meteor, IM1. (Credit: Clif Alferness)

As I left home to jog at sunrise, I saw a group of wild turkeys on the asphalt road ahead. However, my top priority when I leave home is to survey the sky overhead, as I tell my students: “Look up rather than down, because there is much more real estate out there than on our rock, the Earth.” Indeed, I was not disappointed this time around. The sky exhibited an amazing display that was more impressive than the proudest wild turkey on the road, irrespective of how much it ruffled its feathers as I passed by. The view overhead appeared like a giant canvas of a Jackson Pollock’s drip painting. It was covered by a fantastic mix of purple, red and yellow.

At class, a few hours later, I explained to my students that Rayleigh scattering paints the sky with these colors at sunrise and sunset. During these special periods of time, the sun is oriented near the horizon and its light rays traverse a large column of the atmosphere, where the opacity scales inversely with wavelength to the fourth power. While blue light at short wavelengths is scattered, red light at longer wavelengths makes it through. The same scattering process during the daytime makes the entire sky blue. Oceans reflect the color of the sky and appear blue during the day. At nighttime, the Earth blocks the sun and so the sky and the oceans appear black. I explained to my class that because the Earth spins, we have an eclipse of the Sun by the Earth every night. As a result, I am not particularly excited about the rarity of the upcoming solar eclipse at Harvard College on April 8, 2024, because I do not care which particular rock, be it the Earth or the Moon, blocks the Sun.

Understanding exotic phenomena through the laws of physics enhances our appreciation for the beauty of nature, but it also takes away the extraordinary quality that we assign to previously unexplained events. If the burning bush that was never consumed, as witnessed by Moses in the bible, would have been explained as a technological gadget purchased on Amazon, then this object would have lost its extraordinary significance. Scientific understanding transforms the extraordinary into the ordinary. To make this leap we only need evidence, not extraordinary evidence; hence, I disagree with Carl Sagan’s aphorism: “Extraordinary claims require extraordinary evidence.”

And speaking about exotic phenomena, on occasion the darkness of night is lit up by a fireball of a meteor. Such fireballs are currently being reliably monitored by sensors aboard U.S. Government satellites. This network was constructed to detect the flash of heat generated by the launch of ballistic missiles from adversarial nations. On January 8, 2014, the same satellites spotted a meteor over the Pacific Ocean which was moving faster than the escape speed from the solar system. We labeled it IM1, an abbreviation for Interstellar Meteor # 1 (pronounced as “I am one”). On June 14–28, 2023, our expedition team surveyed the ocean floor at IM1’s site, based on the location reported by the U.S. Space Command in NASA’s catalog of fireballs.

Clif Alferness, an engineer and rock carver who has been following the IM1 expedition with interest, wrote to my colleague Mike Williamson yesterday: “Here is my sculpture depicting IM1 entering the earth’s atmosphere. The stone is called Honeycomb Calcite and comes from a quarry high in the mountains of Utah. If you forward it to Avi, please tell him that I have enjoyed following his expedition and look forward to the follow-on work and publications. This piece would not have existed had I not been inspired by his research.”

The discovery of IM1 raises new questions, including: “Where did IM1 come from?” Given the arrival velocity of IM1, I started a calculation with my brilliant Harvard College student, Shokhruz Kakharov, intended to figure out where IM1 originated from — depending on the duration of its journey. Interestingly, IM1 could have started its journey on the opposite side of the Milky-Way disk relative to the Sun if its journey lasted a billion years. For longer travel times, it could have originated from billions of possible stars within the Milky-Way galaxy.

Notes of an analytic derivation regarding the trajectory of an interstellar object which arrives at the Local Standard of Rest of the Milky-Way with some circular velocity shift.

This is good news for interstellar travel, because it implies that our chemical rockets could explore the real estate on billions of habitable planets in the upcoming billions of years before the Sun will die. Similarly, earlier civilizations in the Milky-Way galaxy might have already done it.

The question of whether to invest an annual budget of trillions of dollars in military conflicts or in space exploration relates to whether we look down or up. So far, humanity overwhelmingly prioritized the former over the latter. However, at the Munich Security Conference on February 16, 2024, I argued that survival of the fittest in interstellar space favors civilizations which look beyond the wild turkeys that puff-up feathers on their local political roadmap.

As we concluded our latest meeting yesterday, Shokhruz asked me in his calm and condensed way: “Do you think there are aliens?” “Of Course,” I replied, “…it would be arrogant of us to think that we reside at the intellectual center of the Universe. We should search until we find them. Interstellar objects, like IM1 or the second of its type, IM2 (pronounced “I am too”), could inform us whether the grass is greener in our neighbors’ yards.”

Reality is under no obligation to flatter our ego. And if we find evidence for intriguing neighbors based on interstellar objects, we might change priorities and travel to their yard to say hello. In that case, the computer code that Shokhruz and I are using will become handy as it allows to plan the journey to any destination in the Milky-Way and calculate the expected duration of the trip.


Image credit: Chris Michel (October 2023)

Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. His new book, titled “Interstellar”, was published in August 2023.



Avi Loeb

Avi Loeb is the Baird Professor of Science and Institute director at Harvard University and the bestselling author of “Extraterrestrial” and "Interstellar".