Solar Week - Ask a Question

Come here during Solar Week (next one: March 22-26, 2021) to interact. To post a question, click on your area of interest from the topics below, and then click on the "Ask New Question" button. Or EMAIL or tweet or plant in Answer Garden your question about the Sun or life as a scientist to us -- and watch for it to appear here.  You can also visit our FAQs (frequently asked questions). In between Solar Weeks in October and March, you can view all the archives here.

PrevPrev Go to previous topic
NextNext Go to next topic
Last Post 3/30/2017 8:21 AM by  Kris Sigsbee
Planet Classification
 1 Replies
You are not authorized to post a reply.
Author Messages

Tiny L


3/30/2017 6:22 AM

    Are scientists really thinking about reclassifying earth other than a planet, but like a dwarf-planet? I heard some talk about this a couple days ago. thank you very much
    Tags: Pluto, Earth, orbit, planet, planet classification

    Kris Sigsbee

    Basic Member

    Basic Member

    3/30/2017 8:21 AM

    I am curious where you heard people talking about this. I have not heard anything about scientists re-classifying Earth to be a dwarf planet. I tried a quick Google search and all I could find about this was some discussion among non-scientists interested in astronomy on a Quora message board, a 2011 blog post on a web site I have never heard of before called "Seeker" which appears to be related to the Discovery Channel, and a popular science article from 2011 on io9 that cites well-known NASA and university astronomers involved with creating the new definition of major and dwarf planets.

    There is nothing wrong with discussing astronomy online with your friends, reading blogs about astronomy, and other popular science articles online. However, you need to be careful about the sources of the information, and think about who the authors of this information are. If the authors would be considered experts (have a degree in a STEM field) who work for NASA, a university, or a planetarium, or are journalists who consulted experts to write their article and cite sources, then it is probably a trustworthy source of information. However, if the authors are in the entertainment business, or just ordinary citizens chatting on a message board, they may not be a reliable source of scientific information. It is also important to think about whether or not the author has an agenda, like being really upset about Pluto being demoted to dwarf planet and desperately wanting it reinstated to full planet status, or if the author is an online troll who just likes to stir up controversy.

    The official definition of "planet" adopted by the International Astronomical Union (IAU) in 2006 is a celestial body which:
    is in orbit around the Sun,
    has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
    has "cleared the neighborhood" around its orbit.
    If an object only meets the first two conditions, like Pluto, it is considered a dwarf planet. As the message board discussion and Seeker article I found pointed out, there are many asteroids and other debris along and crossing Earth's orbit, so they tried to argue that Earth should not be a planet. However, the same thing applies to the other planets as well. The key thing here is what scientists meant by the third condition, and is pointed out in the io9 article - it is not the number of objects that matters, but their mass, and what is controlling their orbits. Scientists are still debating the best way to determine this. While there is debris on the orbits of the major planets, the major planets influence the orbits of the other bodies within their orbital zone. Jupiter may have a large number of small objects in its orbit like the Trojan asteroids, but these objects only exist in Jupiter's orbit because they are controlled by Jupiter's gravity. Astronomers have proposed different metrics (or tests) for orbital zone clearance based on the mass of the host star, the mass of the potential planet, the orbital period of the potential planet, the mass of other objects in the vicinity, and the ability of the potential planet to clear its gravitational sphere of influence (called the Hill Sphere) in a certain amount of time. Earth passes these tests, but Pluto does not. There is not really any serious scientific discussion about demoting Earth to dwarf planet status, as far as I know. And there is not really any serious scientific discussion at this point about reinstating Pluto to major planet status.
    You are not authorized to post a reply.

    Twitter Feed

    Scientist Leaderboard

    Name # of replies
    Multiverse skin is based on Greytness by Adammer