Guardian = Liberal socialist = duh
Because it sounds "awesomer," and thus garners more clicks.
Regards,
“Super-earth” is a reference to size — the suspected body is larger than Earth, but not the size of one of the gas giants (Jupiter, Saturn, Uranus, Neptune).
Lots of people have had reason to suspect the existence of one, beginning with the discovery of Uranus (the planets up to and including Saturn have been known since ancient times).
For example, Harrington and Van Flandern calculated a planet 2 to 5 earth-masses was responsible for the disturbed Neptunian moon system; at the time they wrote that paper they also regarded Pluto as an escaped moon of Neptune.
Neptune’s variability from its ephemeris was a one-time event, and led to the search for and discovery of Pluto. Pluto turned out to be too small to account for the disturbance of Neptune, so the search for an unknown has continued. Tombaugh himself surveyed the ecliptic for years after his discovery of Pluto, and was convinced that nothing was there down to something like 12th magnitude.
Pluto’s discovery was a very lucky break, because it’s inclined out of the ecliptic, as are most of the so-called KBOs (my guess is, the Kuiper Belt Object nomenclature will be abandoned in time, at least as applied to these ‘dwarf planets’).
I think there was at least one pre-discovery observation of Pluto found in a survey of older observations (iow, it got missed by someone; the practice of looking for pre-discovery observations helps in determining the orbit of the object with greater precision). Galileo is known to have observed Neptune and not realized it, and some believe that he actually knew it but never got credit for it.
http://www.space.com/6941-theory-galileo-discovered-neptune.html