When Goldilocks entered the cabin of the three bears and tasted the first bowl of porridge, she exclaimed, “this bowl is too hot.” The second bowl “was too cold.” But the third bowl was “just right.”
Mercury and Venus are too close to the Sun, and they are too hot. Mars and the other outer planets are too cold. Luckily for us, the Earth is just the proper distance from the Sun for life to flourish. We orbit the Sun in what is called the Goldilocks, or habitable, zone.
Temperature is not the only necessary condition. The Sun must be stable for a long time for life and society to develop. Not all stars are stable.
Our atmosphere must be thick enough to block harmful solar rays while passing just the correct wavelengths and amounts of light. Not all planets have such a blessed atmosphere. Although Venus is farther from the Sun than the planet Mercury, carbon dioxide in the Venetian atmosphere is a heavy blanket that keeps Venus hotter than Mercury.
Life as we know it requires liquid water. Earth is the only planet or moon in the solar system to be so blessed.
The Sun is not the only star with orbiting planets. Theories of star formation anticipate planets. Confirmation by direct observation of planets around stars is extremely difficult because at the immense distance of stars their planets appear too close to the glare of the star.
Advancing technology developed indirect methods to detect these so-called exoplanets. Astronomers confirmed the first exoplanet in 1988. Since 2009, five ways are available for detecting exoplanets.
The first method is transit. When a planet passes in front of a star, it periodically blocks a tiny portion of light, and this dimming is measurable.
A second method takes advantage of the fact that stars not only pull on orbiting planets, but the planet pulls a little on the star. The resulting stellar wobble can be detected. The other three more complex methods provide additional information about the nature of both the planet and the star.
As of last month, astronomers have confirmed 4,719 exoplanets, with hundreds more found each year.
The current best estimate is that about 1 in 5 stars host a near Earth-sized planet in the Goldilocks zone. With approximately 200 billion stars in the Milky Way, there are about 40 billion planets in the Goldilocks zone. And there are roughly 200 billion galaxies in the observable universe. Of course, to support life, the other conditions must be satisfied. Nevertheless, the number of potentially life-supporting planets is unimaginable.
UFOs have been in the news recently. Are they visitors from other worlds? That’s a whole, more complicated question. Are you curious? This is a topic in my book “Astronomy is Heavenly” available at the Bookshelf in Thomasville, or at Amazon.