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Recently, the existence of a pointlike pertuber PX with$1~m_\textrm{Mars}\lesssim m_\textrm{X}\lesssim 2.4~m_\oplus$ supposedly movingat $65-80~\textrm{AU}$ along a moderately inclined orbit has been hypothesizedin order to explain certain features of the midplane of the Kuiper Belt Objects(KBOs). We preliminarily selected two possible scenarios for such a PX, andnumerically simulated its effect on the Earth-Saturn range $\rho(t)$ by varyingsome of its orbital parameters over a certain time span; then, we compared ourresults with some existing actual range residuals. By assuming $m_\textrm{X} =1~m_\textrm{Mars}$ and a circular orbit, such a putative new member of ourSolar System would nominally perturb $\rho(t)$ by a few km over $\Delta t =12~\textrm{yr}~(2004-2016)$. However, the Cassini spaceraft accurately measured$\rho(t)$ to the level of $\sigma_\rho\simeq 100~\textrm{m}$. Nonetheless, sucha scenario should not be considered as necessarily ruled out since the Cassinidata were reduced so far without explicitly modeling any PX. Indeed, a NASA JPLteam recently demonstrated that an extra-signature as large as 4 km affectingthe Kronian range would be almost completely absorbed in fitting incompletedynamical models, i.e. without PX itself, to such simulated data, thus notshowing up in the standard post-fit range residuals. Larger anomaloussignatures would instead occur for $m_\textrm{X} > 1~m_\textrm{Mars}$. Theirnominal} amplitude could be as large as $50-150~\textrm{km}$ for $m_\textrm{X}= 2.4~m_\oplus$, thus making less plausible their existence.

Is the recently proposed Mars-sized perturber at $65-80~\textrm{AU}$ ruled out by the Cassini ranging data?