\n<\/p>\n
And there are more problems with M star systems. Here on Earth, we have a 24-hour day, which allows our planet to be evenly heated by the sun. This is, surprisingly, not the case for many planets. Consider our moon. We see the same face, no matter the phase, or the time of year, or where we are on Earth. It\u2019s\u00a0tidally locked<\/i>. There are many factors that determine if and when a smaller celestial object will tidally lock to a larger one, but the closer an object is, the faster it will lock. The habitable zone of an M star is far closer in than the habitable zone of our sun, so we anticipate that most of these planets orbit their star the way our moon orbits us: with a permanent dayside and a permanent nightside \u2014 perhaps a more challenging environment for life to arise.<\/p>\n
We live in a pleasant suburb of the Milky Way and orbit a quiet star, but there are also a number of things about our planet itself that make it so amenable to life. Earth has a rocky surface featuring both ocean and land as well as the slow grind of plate tectonics. Besides rearranging the continents every half-billion years or so, plate tectonics also \u2014\u00a0very<\/i> slowly \u2014\u00a0removes carbon dioxide from our atmosphere by burying surface materials the gas has reacted with into the mantle. Our active geology provides us with other benefits as well: Earth\u2019s moving iron-nickel core generates a protective magnetic field. Without it, even the most well-behaved star could slowly erode away the air we breathe.\u00a0<\/p>\n
All of this is to say that when we read a news story that proclaims the discovery of a brand-new habitable zone planet, we cannot, and should not, rush to conclusions. \u201cThe major misconception is the assumption that the habitable zone is a hard and fast rule for habitability,\u201d said Dr. Adeene Denton, a planetary scientist and former Astronomer in Residence at the Grand Canyon. They compared the concept of the habitable zone to \u201cbumpers on a bowling lane\u2026 their role is to guide us to a specific destination.\u201d But, Dr. Denton cautions, even this is an Earth-centric picture. There may very well be life thriving in the\u00a0methane-ethane lakes of Titan,\u00a0the subsurface oceans of moons far outside our habitable zone, or in\u00a0pools of ammonia in other star systems. Without being certain just how unique the Solar System is, it is hard to even judge the utility of the habitable zone.\u00a0<\/p>\n
The concept of habitable-zone planets risks more than Earth-centrism \u2014 it can easily mislead the public. One such finding was\u00a0TOI-700 d, the first habitable-zone Earth-sized planet located by the\u00a0Transiting Exoplanet Survey Satellite. \u201cEvery time you publish a habitable zone planet result, there\u2019s always some reaction about whether or not it\u2019s\u00a0actually inhabited<\/i>,\u201d said Mr. Jonathan Brande, a Ph.D candidate at the University of Kansas who contributed to the discovery. \u201cThere’s a thin line to tread between getting people excited about astronomy and not accidentally confusing them.\u201d TOI-700 d is one of many planets discovered to orbit an M star, so its habitability is far more up for debate than if it orbited a star like our own. Near-term studies of the planet will reveal whether it has an atmosphere, but we will need to wait for the\u00a0Habitable Worlds Observatory of the 2040s to study it in depth, added Mr. Brande.\u00a0<\/p>\n
The narrative given to the public is just as important as the science surrounding habitability. We must remember that the habitable zone is \u2014 as they say \u2014 the beginning of wisdom, not the end, and that wisdom must be handled responsibly, for the good of the field and the people who love it.<\/p>\n<\/div>\n