Recent observations suggest that small, earthlike worlds form a very

Here's the claim the support for which we have to weaken:

earthlike worlds form a very low percentage of the planets orbiting stars in the galaxy other than the sun

Here's the support for that claim:

Of over two hundred planets that astronomers have detected around other stars, almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun.

Notice that the evidence is the characteristics of "planets that astronomers have detected around other stars."

Those characteristics of planets that astronomers have detected are that "almost all are hundreds of times larger and heavier than the earth and orbit stars much smaller than the sun."

So, the reasoning of the argument is basically that, since most planets detected are larger and heavier than the Earth and orbit stars smaller than the Sun, Earthlike worlds form a very low percentage of the planets orbiting stars in the galaxy.

Now, let's consider choice (D).

D. The smaller a planet is relative to the star it orbits, the more difficult it is for astronomers to detect.

At first this information may seem irrelevant to the argument, but if we consider it carefully, we can make the following connection.

Choice (D) says that planets that are small and orbit large stars are hard to detect. So, it may be that the reason most "planets that astronomers have detected" are large and orbit small stars is simply that astronomers have not succeeded in detecting planets like Earth, which are small relative to the stars they orbit.

Thus, (D) shows that the conclusion that "earthlike worlds form a very low percentage of the planets" doesn't necessarily follow from the evidence about "planets that astronomers have detected because the planets astronomers have detected may not be a representative sample of "the planets orbiting stars in the galaxy."


A planet almost the same size as a star would be a very big planet because stars are generally much larger than planets. Also, notice that the argument doesn't say that the detected planets are similar in size to stars. Rather, it says that the planets are "hundreds of times larger and heavier than the earth," meaning that they are still much smaller than stars.

In any case, (D) still works even if some planets are close in size to the stars they orbit because it could still be the case that planets that are small relative to the stars they orbit, as Earth is to the sun, would not be detected.