▲ ‘Ultra Deep Field’ taken by the Hubble Space Telescope in 2014. (Source/NASA, ESA, etc.) Adam Berger, professor of astrophysics at UC San Diego, posted this on the space website Space.com on October 9. We introduced the latest techniques for measuring the ages of stars and planets.
Measuring the ages of planets and stars helps scientists understand when planets formed, how they change, and, in the case of planets, whether life had time to evolve.
Unfortunately, the age of objects in space is difficult to measure. Stars like the Sun maintain the same brightness, temperature and size for billions of years. A planet’s properties, such as temperature, are often determined by the star it orbits rather than its own age and evolution.
Determining the age of a star or planet can be as difficult as guessing the age of a person who looks the same from childhood to retirement.
Estimating the age of a star
Just as dating fossils is key to the study of evolution, determining the age of stars is an important problem in astronomy.
Fortunately, stars change their brightness and color subtly over time. Highly accurate measurements allow astronomers to compare these measurements of a star to a mathematical model that predicts what the star will do as it ages, and from there estimates its age.
Not only do stars shine, but they also rotate. As time goes by, the speed of rotation slows down. This is similar to a spinning wheel slowing down due to friction.
By comparing the rotation rates of stars of different ages, astronomers were able to create a mathematical relationship for the ages of stars, a method known as gyrochronology. This allowed astronomers to measure the age of stars with an error of 10%.
The star’s rotation also creates powerful magnetic fields and generates magnetic activity such as stellar flares, powerful bursts of energy that occur on the star’s surface. The steady decline in a star’s magnetic activity can also help estimate its age.
A more advanced method of determining the age of a star is asteroseismology, the science of studying the internal structure of pulsating stars by the interaction of their frequency spectra.
Astronomers study vibrations on a star’s surface caused by waves passing through the star’s interior. Young stars have different vibration patterns than older stars. Using this method, astronomers estimated the sun’s age to be 4.58 billion years.
The age of a planet is determined by radiometric dating.
In the solar system, radionuclides are key to planetary dating. These are special atoms that release energy slowly over a long period of time. As natural clocks, radionuclides help scientists determine the ages of all kinds of objects, from rocks to bones to ceramics.
Using this method, scientists determined that the oldest known meteorite was 4.57 billion years old, which is roughly the same as the Sun’s astroseismological estimate of 4.58 billion years. The oldest known rock on Earth is slightly younger, at 4.4 billion years old. Likewise, radionuclides from soil retrieved from the Moon during the Apollo missions were up to 4.6 billion years old.▲ Researchers estimate that the Sun is 4.58 billion years old. (Source: NASA) Studying radionuclides is a powerful way to determine the age of a planet, but it is only possible if you have the objects on hand. Typically, astronomers only have pictures of planets.
Astronomers often determine the age of rocky space objects, such as Mars or the Moon, by counting the number of craters. Older surfaces have more craters than younger surfaces. But erosion from water, wind, spacecraft, and volcanic lava flows can erase evidence of previous impacts.
This method is useless for giant planets like Jupiter, which have deeply buried surfaces. But astronomers can estimate the age by counting the number of craters on the moon or studying the distribution of certain types of meteorites scattered by the moon. This is consistent with radionuclides and crater formation methods for rocky planets.
With current technology, it is not yet possible to directly measure the age of planets outside the solar system.
How accurate are these estimates?
The age of our solar system can be measured with the highest accuracy. That’s because astronomers can compare the radionuclide ages of rocks on Earth, the Moon, and asteroids with the astroseismic ages of the Sun, and the two agree very well.
The stars in clusters such as the Pleiades and Omega Centauri are believed to have all formed around the same time. Therefore, the estimated ages of the individual stars in this cluster should be the same. For some stars, astronomers can detect radionuclides in the atmosphere, such as uranium, a heavy metal found in rocks and soil that has been used to determine ages by other methods.
Astronomers believe that planets are about the same age as their host stars, so improving methods for determining the ages of stars could also help determine the ages of planets. By studying these subtle clues, it is possible to estimate the exact age of a star.
Gwangsik Lee, Science Columnist joand999@naver.com
