With thousands of images taken by various probes sent to Mars, it would seem inevitable that unusual or puzzling objects might be seen in some of them. And of course, there have been, most notably the famous "Face on Mars" first seen in low-resolution Viking orbiter images in the 1970s. Higher-resolution images taken later by other orbiters with better cameras showed it, and nearby interesting formations, to be just natural hills and mesas. Despite that, other curious things are seen in both orbital and ground images from time to time, although they almost always have a simple prosaic explanation. Another such oddity was just recently seen in an image taken by the Mars Reconnaissance Orbiter (MRO), which has attracted some attention. Most likely it is a natural rock formation, but it's also not, as described by the tabloid Daily Mail, a "spherule" either.
The image shows a bright object casting a long shadow across the floor of what might be a dried-up lakebed. Some observers have said it might be a tower or spire, judging by the long shadow, but the view is from directly above and not enough detail can be seen on the object itself. The object does stand out for its brightness, but little more can be said about it. Using Occam's Razor, it is most likely a natural geological rock formation, and not an alien tower, but it also can't be a round "spherule" as referred to. The spherules seen by the Opportunity and Curiosity rovers are tiny, only a few millimeters across, way, way too small to be seen from orbit. If at all sphere-shaped, it is much bigger than that. Simply being round or tall also wouldn't prove it was something artificial.
'Tower' or 'sphere' close-up
Spherules on Mars (Opportunity rover)
Spherule on Mars (Curiosity rover)
"A number of straightforward geological processes can yield round shapes," said Dr. Hap McSween, an Opportunity science team member from the University of Tennessee.
On Earth, round objects such as concretions are common, but are completely natural in origin. They are, however, quite small, like their spherule cousins on Mars. A round object the size of what appears in the MRO image would be interesting, but then the Daily Mail article refers to the object being either tall like a tower or round like a ball–a little confusing. A larger spire would also be interesting, but still probably natural, as similar formations can also be found on Earth (and even on Pluto, as discovered by the New Horizons spacecraft - icy penitentes-like structures about 1,600 feet tall!).
The image is reminiscent of the famous and controversial "spires" called the Blair Cuspids, photographed on the Moon by the Lunar Orbiter 2 spacecraft in 1966.
The Curiosity rover has seen a number of weird formations, but they can be best explained by erosion from wind or ancient water. Very thin needle-like rock formations, spherules and even a couple "spoons" have been seen. All have been only a few centimetres at most in size. Such delicate features can last much longer in the thinner atmosphere and lower gravity than they could on Earth. They are uniquely Martian.
'Spoon' on Mars #1 (Curiosity rover)
'Spoon' on Mars #2 (Curiosity rover)
'Needle' on Mars (Curiosity rover)
Blair Cuspids 'spires' on the Moon
'Face on Mars' (Mars Reconnaissance Orbiter/Viking Orbiter)
The tiny spherules seen by the Opportunity rover in particular, composed of hematite, are very similar to concretions on Earth and may have similar origins. They were seen by the thousands, spread over the landscape. The ones seen by Curiosity have been fewer in number and their composition isn't known yet; some have a greenish color to them however, while the Opportunity ones were grayish. Some concretions can be formed with the assistance of water and sometimes microbial life, while others, such as volcanic lapilli, are simply geological.
The lesson here is that just because something looks unusual, does not automatically mean it must be something constructed by aliens. Such a finding would of course be exciting, but extreme caution must always be used, especially in this age of "internet armchair experts" who see artificial objects in practically every image they look at, no matter how fuzzy or pixelated the image may be in many cases (often a case of pareidolia). It also means not jumping to other conclusions as well, such as in this Daily Mail story. There is not enough detail in this one image to tell if the object is round or tall or something in-between. It can be seen however, that it must be much larger than any of the tiny spherules referenced in the story.
We may hopefully one day find solid evidence of alien intelligence, but unfortunately this new image, again, most probably isn't it.
The original MRO image can be seen here.