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Old Sun, New Sun, Our Sun

The Milky Way fills the night sky over Chile's Cerro Paranal, home to the European Southern Observatory's Very Large Telescope (VLT).
The Milky Way fills the night sky over Chile's Cerro Paranal, home to the European Southern Observatory's Very Large Telescope (VLT).

Would you like to see yourself in the future? If you found a magic mirror capable of showing your image one, two or three decades away, would you look? I imagine opinions would be split on the wisdom of gazing into this special reflector.

Seeing the future raises all sorts of complicated issues, including some weird paradoxes that we usually only consider when looking back in time. For example, if I saw myself hugely fat in the future and decided to go on a serious diet, would I lose weight? If I did, wouldn't I be changing the future? Can we interfere with the flow of time? (Superman could, but shouldn't ... ) Would our image disappear if we died? (Cool idea for a short story ... ) Or, who knows, maybe there isn't only one future. There could be multiple futures, each with a different possible path where our choices might have taken us, somewhat like in Jorge Luis Borges's short story The Garden of the Forking Paths. (I'll refrain from going into the multiverse today, or the many worlds interpretation of quantum mechanics. Let's stick to firmer ground.)

Leaving these very human questions aside, the fact is that, at least in astronomy, seeing the future and the past is extremely useful.

In fact, an international team of astronomers, led by Jorge Meléndez from the University of São Paulo in Brazil, has been hunting for stars similar to our 4.6-billion-year-old sun. He's been looking for "twin suns", stars both younger and older than ours, so as to better understand our own mother-star.

The group uses the European Southern Observatory's Very Large Telescope (VLT), nested in the heights of Chile's Cerro Paranal. As you read these lines, I'll be up there visiting the VLT and shooting a documentary about science and faith. Stay tuned for more on that next week.

In an article from April published in The Astrophysical Journal Letters, the group reports having found two twin-suns. One, 18 Scorpii, is much younger, at 2.9-billion years, while the other, HIP 102152, at 8.2-billion years, is much older. So, we now have an eye on our sun's past and another on its future.

The essential question is whether our sun is a typical — or an atypical — star. That is, will it keep on producing its energy for the foreseeable future in the manner to which we are accustomed.

Recall that stars like our sun produce energy as they fuse hydrogen into helium at their cores, reaching temperatures of about 30 million degrees Fahrenheit. If the sun is an atypical star, it could go into some sort of imbalance, either increasing or decreasing its fusion rate. Both situations would be catastrophic for life on Earth.

It's always good to remember that we owe our lives to the magnanimity of the sun.

The research group found, fortunately, that our sun is a typical star. Seeing its older twin is like seeing what will be going on some 3.6-billion years from now. The article, with first author TalaWanda Monroe, also from the University of São Paulo, describes the amount of lithium in the three stars, showing that there is a simple correlation between stellar age and the lithium abundance: the older the star, the less lithium it has.

The authors also note that HIP 102152 doesn't seem to have any gas giant planet near its habitable zone (the zone where life would have a higher chance of being found). This makes it sound promising for the existence of rocky planets like the Earth and Mars.

It's hard not to fantasize about what kind of life could exist on a rocky, Earth-like planet circling such an old star. Imagine if this life had reached a level of self-awareness and high intelligence. It might have been there for eons when compared to our own presence here on Earth, spanning a mere 200,000 years.

If we are smart enough to survive our destructive tendencies, where might we be one-, two-, four-billion years from now? Would we even be human, or something completely different, perhaps not even material (in the sense of having a body)?

HIP 102152 is "only" 250 light-years from us. If there is advanced life there, it has never come to see us. Or, if it has, it left without leaving any obvious clues to the visit. Perhaps, with old age comes the wisdom to respect other cultures, the intelligence to leave them alone and, at most, observe them from afar.

You can keep up with more of what Marcelo is thinking on Facebook and Twitter: @mgleiser

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Marcelo Gleiser is a contributor to the NPR blog 13.7: Cosmos & Culture. He is the Appleton Professor of Natural Philosophy and a professor of physics and astronomy at Dartmouth College.