exoplanet
NASAは、欧米の国際共同研究チームが、地球と似た質量を持つ惑星を７つ発見したことを発表しました。そのうち３つは居住可能であるとのことです。
Astronomers discover 7 potentially habitable exoplanets orbiting nearby dwarf star
An international team of astronomers has discovered seven potentially habitable exoplanets -- or planets outside our solar system -- that could have liquid water on their surfaces, according to a paper published today in the journal Nature.
"The discovery gives us a hint that finding a second Earth is not just a matter of if, but when," Thomas Kutcher, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington, said at a news conference today.
It is also a major step forward in answering the age-old question of "Are we alone out there?" Kutcher added.
Though it is unclear whether any of the newly discovered planets can harbor life, astronomers said all seven exoplanets could have liquid water -- the key to life as we know it.
The newly discovered planets have been nicknamed "Earth's seven sisters" and have masses similar to that of Earth's, in addition to having rocky compositions like our planet, scientists said.
Three of the seven planets are considered to be in the habitable zone, which is the area around a star where a rocky planet is most likely to have liquid water, researchers added.
気になった単語は、"exoplanet"です。"planet"が付いているので惑星の種類の総称を指していることは想像がつきます。
『ジーニアス英和辞典』第４版（大修館）で確認してみると、「太陽系外惑星」と載っていました。
また、"exo"には「外の」という意味があります。
LDOCEでは、"a planet that is not in the solar system"と表現されています。
約40光年先という、比較的太陽系から近い宇宙で地球に似た惑星を７つも発見したのは初めてとのことで、歴史的な大発見と言えます。(Akim)
