It seems that the MAST Portal advanced search for moving targets (advertised in the recent MAST Newsletter) suffers from the same problem as the "MAST classic" search. If you rely on Target Name you will miss many archive entries, since proposers could name their targets anything, e.g. the target names for Jupiter observations are often abbreviated, have suffixes, etc, and would not be found by a search with the string "jupiter".
For example, a MAST Classic search for WFPC2 "*jup*" returns 2257 entries, but a MAST Portal WFPC2 "jupiter" search returns 1948 -- and I suspect it is really smaller than that, since there seem to be redundant entries for PC and WFC apertures for the same WFPC2 observations. My pilot Planet Pipeline search (which is WFPC2-only, and where we standardized target names for exactly this reason) returns 2277 entries -- closer to the MAST Classic wildcard search. Apparently MAST Portal doesn't allow wildcards in the Target Name field?
I had been hoping to expand the following HST moving target search page to include other HST instruments, but I'd be happy to put that effort into advising on the MAST Portal interface instead (which could benefit the data from other missions too): https://archive.stsci.edu/prepds/planetpipeline/search.php
On a related note, if MAST could ingest planetary metadata for each HST moving target, as we did for Planet Pipeline, and make that queryable too, it would really be a boon for planetary science archival research with MAST.